66th BPSC Prelims 2020 Part 2 Question Paper with Answers and Solutions (Solved)

🌡️ Infrared Radiation and Its Therapeutic Uses

Infrared (IR) radiation is commonly used in physiotherapy for the treatment of muscle ache, stiffness and certain types of joint pain. When infrared radiation is absorbed by body tissues, it produces a heating effect. This superficial heat can increase local blood circulation, relax muscles and provide temporary relief from pain and stiffness. Infrared therapy is also known as a form of heat therapy or thermotherapy.

🔬 How Does Infrared Therapy Work?

Infrared radiation transfers energy to the exposed tissues, producing heat. The resulting temperature increase causes local blood vessels to dilate, a process known as vasodilation. Improved circulation can increase the supply of oxygen and nutrients to the treated area. The warmth may also reduce muscle tension and make movement more comfortable. However, infrared therapy mainly provides symptomatic relief and does not necessarily treat the underlying cause of muscle pain.

📊 Comparison of Important Electromagnetic Radiations

📚 Important Facts About Infrared Radiation

• Discovery: Infrared radiation was discovered by William Herschel in 1800.
• Position: It lies beyond the red end of the visible spectrum and before microwaves in the electromagnetic spectrum.
• Wavelength: Its approximate wavelength range is 700 nanometres to 1 millimetre.
• Nature: Infrared radiation is an electromagnetic wave and can travel through a vacuum.
• Sources: The Sun, fire, heated objects and human bodies emit infrared radiation.
• Remote sensing: Infrared imaging is used to detect temperature differences and monitor vegetation, land surfaces and atmospheric conditions.
• Precaution: Excessive or improperly applied heat may cause burns. Infrared treatment should be used under appropriate professional guidance.

🧠 Quick Revision: Electromagnetic Spectrum

In order of increasing frequency, the electromagnetic spectrum is: Radio waves → Microwaves → Infrared → Visible light → Ultraviolet → X-rays → Gamma rays. Frequency increases while wavelength decreases along this sequence.

✔️ Final Answer: (A) Infrared radiation

⚡ Resistance in a Parallel Circuit

The correct answer is 4.70 kilo-ohm. In a parallel combination, the reciprocal of the equivalent resistance is equal to the sum of the reciprocals of the individual resistances. The equivalent resistance of two parallel resistors is always less than the smaller individual resistance.

🧮 Step-by-Step Calculation

Given:

• Total resistance, R = 1.403 kΩ
• First resistance, R₁ = 2.0 kΩ
• Second resistance, R₂ = ?

Formula for two resistors in parallel:

1/R = 1/R₁ + 1/R₂

Substituting the given values:

1/1.403 = 1/2 + 1/R₂

Rearranging the equation:

1/R₂ = 1/1.403 − 1/2

Taking the LCM and simplifying:

1/R₂ = (2 − 1.403)/(2 × 1.403)

1/R₂ = 0.597/2.806

Therefore:

R₂ = 2.806/0.597 ≈ 4.70 kΩ

Hence, the second resistor has a resistance of approximately 4.70 kilo-ohm.

📊 Series and Parallel Combination: Comparison

🔍 Important Related Concepts

• Ohm’s Law: At constant physical conditions, the potential difference across a conductor is directly proportional to the current through it. V = IR.
• SI unit: The SI unit of electrical resistance is the ohm (Ω).
• 1 kilo-ohm: 1 kΩ = 1,000 Ω.
• Parallel connection: Every resistor has the same potential difference across it.
• Current division: In a parallel circuit, a branch with lower resistance carries greater current, for the same potential difference.
• Household wiring: Electrical appliances are generally connected in parallel so that each receives the required voltage and can operate independently.
• Conductance: Conductance is the reciprocal of resistance. Its SI unit is siemens (S).

Quick Revision: Series → resistances are added; Parallel → reciprocals are added; parallel equivalent resistance is always smaller than the smallest branch resistance.

✔️ Final Answer: (D) 4.70 kilo-ohm

🌡️ Effect of Temperature on Semiconductor Resistance

On heating, the resistance of a semiconductor generally decreases. Semiconductors such as silicon and germanium have a negative temperature coefficient of resistance over their usual operating range. As temperature increases, more electrons gain sufficient thermal energy to move from the valence band to the conduction band, leaving behind holes in the valence band. Consequently, the number of charge carriers increases and electrical conductivity rises, causing resistance to decrease.

🔬 Why Does Resistance Decrease?

At low temperatures, a semiconductor has relatively few free charge carriers. When it is heated, thermal energy breaks some covalent bonds and generates additional electron-hole pairs. Both electrons and holes contribute to the conduction of electric current. The increase in charge-carrier concentration generally dominates the effect of increased scattering, so the overall conductivity increases and resistance decreases.

Conductivity relationship:

σ = 1/ρ

Here, σ represents electrical conductivity and ρ represents resistivity. For a semiconductor, resistivity generally decreases as temperature increases; therefore, conductivity increases.

📊 Temperature Coefficient: Comparison of Materials

💡 Important Semiconductor Concepts

• Semiconductor: A material whose electrical conductivity lies between that of a conductor and an insulator under specified conditions.
• Examples: Silicon (Si) and Germanium (Ge) are important elemental semiconductors.
• Intrinsic semiconductor: A pure semiconductor in which electrons and holes are generated in equal numbers.
• Extrinsic semiconductor: A semiconductor whose conductivity is modified by adding controlled impurities through doping.
• N-type semiconductor: Formed by doping with donor impurities; electrons are the majority charge carriers.
• P-type semiconductor: Formed by doping with acceptor impurities; holes are the majority charge carriers.
• Band gap: The energy gap between the valence band and conduction band determines important electrical properties of a semiconductor.
• Applications: Semiconductors are used in diodes, transistors, integrated circuits, solar cells, LEDs and computer processors.

🧠 Important Exam Comparison

Metals: Heating generally increases resistance because lattice vibrations increase and obstruct the movement of electrons. Semiconductors: Heating generally decreases resistance because the number of charge carriers increases substantially.

✔️ Final Answer: (B) Decreases

⚡ Faraday Constant (F)

The Faraday constant is a universal physical constant representing the magnitude of electric charge carried by one mole of elementary charges. It is approximately 96,485 coulombs per mole (C mol⁻¹). It is obtained by multiplying the Avogadro constant by the elementary charge. Its value does not depend on the amount of electrolyte, the current passed through it or the volume of solvent.

🧮 Formula and Numerical Value

Faraday constant:

F = N_A × e

Where:

• F = Faraday constant
• N_A = Avogadro constant, approximately 6.022 × 10²³ mol⁻¹
• e = Elementary charge, approximately 1.602 × 10⁻¹⁹ coulomb

Therefore:

F ≈ 96,485 C mol⁻¹

This means that one mole of electrons carries approximately 96,485 coulombs of electric charge. The Faraday constant is a fixed physical constant; it is not the same as the amount of electricity actually passed through a particular electrolyte during an experiment.

🔬 Faraday’s Laws of Electrolysis

The Faraday constant is particularly important in electrochemistry and is used in calculations involving the mass of substances deposited or liberated during electrolysis.

• First law: The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electric charge passed through the electrolyte, provided the relevant conditions remain constant.
• Second law: When the same quantity of electricity passes through different electrolytes, the masses of substances deposited are proportional to their equivalent weights.

📊 Important Electrochemical Formulae

In the mass-deposition formula, M is the molar mass of the substance, I is current in amperes, t is time in seconds and n is the number of electrons exchanged per ion in the electrode reaction.

🧪 Example: Electrolysis of Copper Sulphate

During electrolysis of copper sulphate solution using suitable electrodes, copper ions can gain two electrons and deposit as copper metal:

Cu²⁺ + 2e⁻ → Cu

One mole of copper ions requires two moles of electrons for complete deposition. Therefore, the charge required is approximately 2F = 192,970 C. This illustrates how the Faraday constant connects electric charge with chemical change.

🧠 Important Exam-Oriented Facts

• Named after: Michael Faraday, the scientist known for major contributions to electrochemistry and electromagnetism.
• Unit: Coulomb per mole (C mol⁻¹).
• Value: Approximately 96,485 C mol⁻¹.
• One Faraday: The magnitude of charge associated with one mole of electrons.
• Not dependent on: Electrolyte quantity, current or solvent volume.
• Applications: Electroplating, electrolysis, battery calculations and electrochemical measurements.
• Important distinction: Faraday constant is a physical constant, whereas the quantity of charge Q passed in an experiment depends on current and time: Q = It.

Quick Revision: F = N_Ae ≈ 96,485 C mol⁻¹; Q = It; one Faraday = charge of one mole of electrons.

✔️ Final Answer: (D) Is a universal constant

🌌 Light-Year: A Unit of Astronomical Distance

A light-year is a unit of distance, not time. It is defined as the distance travelled by light in a vacuum in one Julian year (365.25 days). Since light travels at approximately 299,792,458 metres per second in a vacuum, one light-year is approximately 9.46 trillion kilometres, or 9.46 × 10¹² km.

🧮 Calculation of One Light-Year

Speed of light:

c = 299,792,458 m/s

One Julian year:

365.25 × 24 × 60 × 60 = 31,557,600 seconds

Distance = Speed × Time

1 light-year = c × 31,557,600

≈ 9.461 × 10¹⁵ metres

Therefore:

1 light-year ≈ 9.461 trillion kilometres

🌠 Why Is a Light-Year Used?

Astronomical distances are extremely large, so kilometres are inconvenient for expressing distances between stars and galaxies. Light-years provide a more convenient unit for describing such distances. For example, when we say that a star is 10 light-years away, its light takes approximately 10 years to reach us. Thus, observing a distant object also means observing light that left it in the past.

📊 Important Astronomical Distance Units

🔭 Important Examples and Facts

• Sun to Earth: Sunlight takes approximately 8 minutes 20 seconds to reach Earth; the distance is about 1 AU.
• Moon to Earth: Light takes approximately 1.3 seconds to travel from the Moon to Earth.
• Proxima Centauri: It is the nearest known star to the Sun, at approximately 4.24 light-years away.
• Milky Way: The diameter of the Milky Way’s main stellar disk is commonly estimated at roughly 100,000 light-years, although its outer structures extend farther.
• Observable Universe: Its present-day observable radius is approximately 46.5 billion light-years because the universe has expanded while the light was travelling.
• Speed of light: In vacuum, the speed of light is exactly 299,792,458 m/s in the SI system.
• Important distinction: A light-year measures distance; a year measures time; metres per second measure speed.

🧠 Common Exam Confusion

The word “year” in light-year often creates confusion, but it only indicates the time used to calculate the distance travelled by light. A light-year is not a measure of time. Similarly, a light-second is the distance light travels in one second, not a time unit.

Quick Revision: Light-year → Distance; 1 light-year ≈ 9.46 × 10¹² km; 1 parsec ≈ 3.26 light-years; 1 AU ≈ 149.6 million km.

✔️ Final Answer: (C) Distance

🌈 Change in Properties of Light Between Two Media

When light travels from one medium to another, its frequency remains unchanged. However, its velocity and wavelength change because the optical properties of the new medium are different. The frequency is determined by the source of light and remains constant at the boundary between two stationary media.

📐 Why Does Frequency Remain Constant?

Light is an electromagnetic wave. When it crosses the boundary between two media, the oscillations must remain continuous at the boundary. Therefore, the number of wave cycles passing a fixed point per second remains the same. Since frequency does not change, the change in velocity produces a corresponding change in wavelength according to the wave equation:

v = fλ

Here, v = velocity of light in the medium, f = frequency, and λ = wavelength. Since frequency remains constant, wavelength changes in the same proportion as velocity.

📊 Changes in Light When It Enters Another Medium

🔬 Important Formulae and Concepts

• Refractive index: The absolute refractive index of a medium is given by n = c/v, where c is the speed of light in vacuum and v is its speed in that medium.
• Wavelength in a medium: It is given by λ = v/f. A decrease in velocity produces a decrease in wavelength when frequency is constant.
• Snell’s law: n₁ sin i = n₂ sin r, where i is the angle of incidence and r is the angle of refraction.
• Optically denser medium: Light travels more slowly in a medium having a higher refractive index.
• Optically rarer medium: Light travels faster in a medium having a lower refractive index.
• Normal incidence: When light enters another medium perpendicular to the surface, its direction does not change, although its speed and wavelength may change.

🧠 Important Exam-Oriented Facts

• The speed of light in vacuum is approximately 3 × 10⁸ m/s.
• The refractive index of vacuum is exactly 1.
• The refractive index of air is approximately 1.0003 under ordinary conditions.
• When light travels from air into glass, its velocity and wavelength decrease, but its frequency remains unchanged.
• When light travels from glass into air, its velocity and wavelength increase, but its frequency remains unchanged.
• The phenomenon of bending of light when it passes from one medium to another is called refraction.

Quick Revision: At a boundary between two media → Frequency remains constant; velocity and wavelength generally change; refractive index is a property of the medium.

✔️ Final Answer: (C) Frequency

⚡ Velocity of Electromagnetic Waves

Electromagnetic waves travel in vacuum at a constant speed of approximately 3 × 10⁸ metres per second (m/s). This is the speed of light in vacuum, represented by the symbol c. The exact value is 299,792,458 m/s. Therefore, option (A) is correct.

🌟 What Are Electromagnetic Waves?

Electromagnetic waves consist of oscillating electric and magnetic fields. These fields are perpendicular to each other and also perpendicular to the direction of propagation. Electromagnetic waves are transverse waves and do not require a material medium for propagation. They can travel through vacuum.

📊 Electromagnetic Spectrum

📐 Important Formulae

• Speed of light in vacuum: c = 299,792,458 m/s.
• Approximate value: c ≈ 3 × 10⁸ m/s.
• Wave equation: c = fλ, where f is frequency and λ is wavelength in vacuum.
• Refractive index: n = c/v, where v is the speed of light in a medium.
• Energy of a photon: E = hf, where h is Planck’s constant and f is frequency.

🧠 Further Exam-Oriented Facts

• Electromagnetic waves were theoretically predicted by James Clerk Maxwell.
• Heinrich Hertz experimentally demonstrated electromagnetic waves.
• James Clerk Maxwell showed that light is an electromagnetic wave.
• All electromagnetic waves travel at the same speed in vacuum, regardless of their frequency or wavelength.
• In a material medium, the speed of electromagnetic waves is generally lower than in vacuum.
• Electromagnetic waves carry energy and momentum and can exert radiation pressure.
• In the electromagnetic spectrum, frequency increases from radio waves towards gamma rays, while wavelength decreases.

Quick Revision: Electromagnetic waves → transverse waves → no material medium required → vacuum speed = 3 × 10⁸ m/s.

✔️ Final Answer: (A) 3×10⁸ ms⁻¹

🌕 Neil Armstrong and the First Moon Landing

Neil Armstrong was the first human being to step onto the surface of the Moon. He achieved this historic milestone on 21 July 1969 (UTC) during NASA’s Apollo 11 mission. In the United States, the landing and first moonwalk are commonly dated 20 July 1969 because of the time difference. Armstrong was followed onto the lunar surface by Edwin “Buzz” Aldrin.

🚀 Apollo 11 Mission: Important Details

• Launch date: 16 July 1969.
• Launch vehicle: Saturn V rocket.
• Launch site: Kennedy Space Center, Florida, USA.
• Lunar landing: 20 July 1969 (UTC).
• First human step on the Moon: 21 July 1969 (UTC).
• Lunar module: Eagle.
• Command and service module: Columbia.
• Mission commander: Neil Armstrong.
• Lunar module pilot: Edwin “Buzz” Aldrin.
• Command module pilot: Michael Collins.
• Return to Earth: 24 July 1969.

👨‍🚀 Apollo 11 Astronauts and Their Roles

🌍 Important Space Exploration Milestones

• First artificial satellite: Sputnik 1, launched by the Soviet Union on 4 October 1957.
• First human in space: Yuri Gagarin of the Soviet Union, on 12 April 1961, aboard Vostok 1.
• First woman in space: Valentina Tereshkova of the Soviet Union, on 16 June 1963.
• First spacewalk: Alexei Leonov of the Soviet Union, on 18 March 1965.
• First human on the Moon: Neil Armstrong, in 1969.
• First woman to walk on the Moon: No woman had walked on the Moon as of November 2026.

🇮🇳 India’s Lunar Exploration

• Chandrayaan-1: India’s first lunar mission, launched on 22 October 2008. It contributed to the discovery of evidence of water molecules on the Moon.
• Chandrayaan-2: Launched on 22 July 2019. Its orbiter continues to provide important lunar observations; the lander did not achieve a soft landing.
• Chandrayaan-3: Launched on 14 July 2023 and achieved a successful soft landing on 23 August 2023.
• Landing site: Near the lunar south polar region, named Shiv Shakti Point by India.
• National recognition: India celebrates 23 August as National Space Day to commemorate the Chandrayaan-3 landing.

Quick Revision: Apollo 11 → 1969 → Neil Armstrong (first) → Buzz Aldrin (second) → Michael Collins (lunar orbit).

✔️ Final Answer: (B) Neil Armstrong

⚛️ Number of Neutrons in a Plutonium Nuclide

The number of neutrons in an atom is calculated by subtracting its atomic number from its mass number. For the given plutonium nuclide, the mass number is 242 and the atomic number is 94. Therefore:

Number of neutrons = Mass number − Atomic number

N = 242 − 94 = 148

Hence, the nucleus of plutonium-242 contains 148 neutrons. The correct answer is option (B).

🔬 Understanding Atomic Number and Mass Number

• Atomic number (Z): The number of protons present in the nucleus of an atom. For plutonium, Z = 94.
• Mass number (A): The total number of protons and neutrons present in the nucleus.
• Number of neutrons (N): The difference between the mass number and atomic number.
• Formula: A = Z + N, or N = A − Z.
• Neutral atom: In an electrically neutral atom, the number of electrons equals the number of protons.

📊 Structure of Plutonium-242

☢️ Important Facts About Plutonium

• Symbol: Pu.
• Atomic number: 94.
• Element category: Actinide series.
• Periodic table: f-block element.
• Discovery: Plutonium was first produced and identified in 1940 by Glenn T. Seaborg and his team at the University of California, Berkeley.
• Name: It was named after Pluto, following the naming pattern of uranium (Uranus) and neptunium (Neptune).
• Radioactivity: Plutonium is radioactive and has several isotopes, including plutonium-238, plutonium-239 and plutonium-242.
• Uses: Certain plutonium isotopes are used in nuclear research, specialised nuclear fuels and radioisotope power systems.

🧠 Related Nuclear Chemistry Concepts

• Isotopes: Atoms of the same element having the same atomic number but different mass numbers. For example, plutonium-239 and plutonium-242.
• Isobars: Atoms of different elements having the same mass number but different atomic numbers.
• Isotones: Atoms of different elements having the same number of neutrons.
• Isomers: Nuclei having the same atomic number and mass number but different nuclear energy states.
• Alpha decay: The emission of an alpha particle reduces the mass number by 4 and the atomic number by 2.
• Beta-minus decay: A neutron changes into a proton, so the atomic number increases by 1 while the mass number remains unchanged.

Quick Revision: Neutrons = Mass number − Atomic number; plutonium-242 → 242 − 94 = 148 neutrons.

✔️ Final Answer: (B) 148

🍯 Viscosity and Its Meaning

Honey has the highest viscosity among the given options under ordinary comparable conditions. Viscosity is the property of a fluid by which it resists the relative motion of its adjacent layers. In simple terms, it measures a fluid’s resistance to flow. Honey flows more slowly than water and blood because it has much greater viscosity.

🔬 What Is Viscosity?

When one layer of a fluid moves over another layer, an internal frictional force develops between them. This resistance to flow is called viscosity. A fluid with high viscosity flows slowly, whereas a fluid with low viscosity flows easily.

For a Newtonian fluid, Newton’s law of viscosity is expressed as:

τ = μ (du/dy)

Here, τ = shear stress, μ = dynamic viscosity, and du/dy = velocity gradient perpendicular to the direction of flow. The SI unit of dynamic viscosity is pascal-second (Pa·s), which is equivalent to N·s/m².

📊 Comparison of the Given Substances

🌡️ Factors Affecting Viscosity

• Temperature in liquids: The viscosity of most liquids decreases when temperature increases. Heating honey makes it flow more easily.
• Temperature in gases: The viscosity of most gases increases with increasing temperature, unlike the usual behaviour of liquids.
• Nature of the fluid: Molecular structure and intermolecular interactions influence viscosity.
• Pressure: Pressure can affect viscosity, particularly in liquids under high-pressure conditions.
• Concentration: In solutions and suspensions, increasing the concentration of dissolved or suspended material may increase viscosity.

🧠 Important Exam-Oriented Facts

• Viscosity: Resistance offered by a fluid to flow.
• Dynamic viscosity: SI unit is Pa·s.
• Kinematic viscosity: It is the ratio of dynamic viscosity to density. Its SI unit is m²/s.
• Fluidity: It is the reciprocal of dynamic viscosity; greater viscosity means lower fluidity.
• Newtonian fluid: A fluid whose shear stress is directly proportional to the velocity gradient at a given temperature and pressure.
• Non-Newtonian fluid: A fluid whose viscosity or flow behaviour does not follow the simple Newtonian relationship; blood and some concentrated suspensions show non-Newtonian behaviour.
• Examples of highly viscous materials: Honey, glycerine and thick syrups.
• Examples of low-viscosity fluids: Water and many gases, although exact comparisons depend on temperature and pressure.

⚠️ Important Scientific Note

Viscosity depends on temperature and, in some cases, pressure and the rate of deformation. Therefore, a strict numerical comparison requires specified measurement conditions. However, in this standard general-science MCQ, honey is clearly the intended answer because it is much more resistant to flow than water, air or ordinary blood.

Quick Revision: Viscosity = resistance to flow; honey → high viscosity; water → comparatively low viscosity; SI unit of dynamic viscosity → Pa·s.

✔️ Final Answer: (D) Honey

🥛 Milk and Its Nutritional Composition

Milk is a nutrient-rich food and an important source of calcium, high-quality protein, fat and carbohydrates. However, ordinary cow’s milk is a poor source of vitamin C. Therefore, the correct answer is Vitamin C. Milk contains lactose, a naturally occurring milk sugar, and provides essential nutrients required for growth, bone development and body maintenance.

📊 Major Nutrients Present in Milk

🧬 Important Facts About Milk

• Main carbohydrate: Lactose, a disaccharide made up of glucose and galactose.
• Main milk proteins: Casein and whey proteins. Casein forms the major proportion of milk protein.
• Major mineral: Calcium, which is essential for healthy bones and teeth.
• Vitamin C: Milk naturally contains very little vitamin C compared with fruits and vegetables.
• Lactose intolerance: It occurs when the small intestine produces insufficient lactase enzyme to digest lactose properly.
• Pasteurisation: A heat-treatment process used to reduce harmful microorganisms in milk. It does not make milk completely sterile.
• Vitamin D: Some milk products are fortified with vitamin D, depending on the country and product.

🍊 Sources of Vitamin C

Good dietary sources of vitamin C include amla, guava, citrus fruits, lemon, oranges, tomatoes and many green vegetables. Vitamin C is important for collagen synthesis, wound healing, antioxidant protection and improving the absorption of non-haem iron.

Quick Revision: Milk → Calcium and protein; main carbohydrate → Lactose; major milk proteins → Casein and whey; poor source → Vitamin C.

✔️ Final Answer: (C) Vitamin C

🚔 Chemical Principle of the Alcohol Breath Test

The traditional chemical breath-testing method uses acidified potassium dichromate (potassium dichromate and sulfuric acid) to detect alcohol vapour in a person’s breath. Ethanol present in exhaled air is oxidised, while the orange dichromate ion is reduced to green chromium(III) ions. The resulting colour change indicates the presence of alcohol. Therefore, the correct answer is Option (A).

🧪 Chemical Reaction

In the traditional test, ethanol is oxidised by acidified potassium dichromate. A simplified reaction showing oxidation to ethanoic acid is:

3C₂H₅OH + 2K₂Cr₂O₇ + 8H₂SO₄ → 3CH₃COOH + 2Cr₂(SO₄)₃ + 2K₂SO₄ + 11H₂O

The important observation is the colour change:

⚗️ Oxidation and Reduction

• Oxidation: Ethanol loses electrons and is converted into an oxidised product.
• Reduction: Chromium in dichromate changes from oxidation state +6 to +3.
• Oxidising agent: Potassium dichromate accepts electrons and causes oxidation of ethanol.
• Acidic medium: Sulfuric acid provides the conditions required for the reaction.

📊 Traditional Chemical Test and Modern Breath Analysers

🧠 Further Exam-Oriented Facts

• Ethanol: Chemical formula C₂H₅OH; it is the alcohol found in alcoholic beverages.
• Potassium dichromate: Chemical formula K₂Cr₂O₇; it is an orange-coloured oxidising agent.
• Chromium oxidation states: Chromium is in the +6 oxidation state in dichromate and the +3 state in the reduced product.
• Breath analyser: Modern devices commonly use electrochemical fuel-cell sensors or infrared technology to estimate alcohol concentration.
• Blood Alcohol Concentration (BAC): It refers to the amount of alcohol present in a person’s blood, generally expressed as a concentration.
• Indian legal limit: Under Section 185 of the Motor Vehicles Act, 1988, the specified threshold is more than 30 mg of alcohol per 100 ml of blood, detected through a breath analyser or other prescribed test.
• Safety: The traditional dichromate reagent contains toxic chromium(VI) compounds and corrosive sulfuric acid; it is a laboratory chemical system, not a substance to handle casually.

Quick Revision: Alcohol breath test (traditional) → Acidified potassium dichromate → Orange to green → Ethanol oxidation and dichromate reduction.

✔️ Final Answer: (A) Potassium dichromate–sulfuric acid

🍇 Alcoholic Fermentation and Zymase

Glucose is converted into ethyl alcohol (ethanol) and carbon dioxide by the process of alcoholic fermentation. This process is carried out by enzymes present in yeast, traditionally referred to collectively as zymase. Therefore, the correct answer is Option (C) Zymase. The process generally takes place under anaerobic conditions, meaning in the absence or very limited availability of oxygen.

🧪 Chemical Equation of Alcoholic Fermentation

The overall reaction can be represented as:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

One molecule of glucose produces two molecules of ethanol and two molecules of carbon dioxide. The carbon dioxide released during fermentation causes the dough to rise in bread-making and is also responsible for bubbles in fermented beverages.

⚙️ Steps Involved in Fermentation

1. Glycolysis: Glucose is broken down into two molecules of pyruvate in the cytoplasm, producing a net gain of two ATP molecules.
2. Decarboxylation: Pyruvate is converted into acetaldehyde, releasing carbon dioxide. The enzyme pyruvate decarboxylase participates in this step.
3. Reduction: Acetaldehyde is reduced to ethanol by alcohol dehydrogenase, using NADH and regenerating NAD⁺.
4. Continuation of glycolysis: Regenerated NAD⁺ allows glycolysis to continue when oxygen is unavailable or limited.

📊 Important Enzymes and Their Functions

🍞 Uses of Alcoholic Fermentation

• Brewing industry: Yeast converts sugars into ethanol and carbon dioxide during the production of alcoholic beverages.
• Bread-making: Carbon dioxide released by yeast makes the dough expand and become porous.
• Bioethanol: Ethanol produced by fermentation can be used as a renewable fuel or blended with petrol.
• Food industry: Fermentation is used in the preparation of several food products and in certain industrial processes.
• Microorganism: Saccharomyces cerevisiae, commonly called baker’s yeast or brewer’s yeast, is widely used for alcoholic fermentation.

🧠 Further Exam-Oriented Facts

• Fermentation: An anaerobic metabolic process that releases energy from sugars.
• Net ATP yield: Alcoholic fermentation itself does not produce additional ATP beyond the two ATP generated during glycolysis per glucose molecule.
• Yeast: A unicellular fungus; Saccharomyces cerevisiae is an important industrial species.
• Lactic acid fermentation: In certain bacteria and animal muscle cells under oxygen-limited conditions, pyruvate is converted into lactate instead of ethanol.
• Louis Pasteur: His work established the important role of microorganisms in fermentation and helped develop modern microbiology.
• Important distinction: Zymase is a traditional collective term for a group of yeast enzymes; it is not a single enzyme responsible for every individual step of the pathway.

Quick Revision: Glucose → Pyruvate → Acetaldehyde → Ethanol; yeast → Saccharomyces cerevisiae; traditional enzyme term → Zymase; by-product → CO₂.

✔️ Final Answer: (C) Zymase

🧪 Limewater Test for Carbon Dioxide

Carbon dioxide (CO₂) turns limewater milky because it reacts with calcium hydroxide to form insoluble calcium carbonate, a white precipitate. This characteristic reaction is commonly used as a laboratory test for carbon dioxide. Therefore, the correct answer is Option (B) CO₂.

⚗️ Chemical Reaction

Limewater is a clear, dilute aqueous solution of calcium hydroxide, Ca(OH)₂. When carbon dioxide is passed through it, insoluble calcium carbonate is formed:

Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O

The white precipitate of calcium carbonate makes the solution appear milky. The downward arrow (↓) indicates the formation of an insoluble solid precipitate.

🔬 What Happens When Excess CO₂ Is Passed?

If excess carbon dioxide is passed through the milky limewater, the calcium carbonate reacts further with carbon dioxide and water to form soluble calcium bicarbonate. As a result, the milkiness gradually disappears.

CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂

This is an important distinction in laboratory experiments: a limited quantity of CO₂ produces milkiness, whereas excess CO₂ can make the solution clear again.

📊 Important Gases and Their Chemical Tests

🌍 Further Exam-Oriented Facts

• Limewater: A dilute aqueous solution of calcium hydroxide, Ca(OH)₂.
• Slaked lime: Calcium hydroxide, commonly produced by adding water to quicklime (calcium oxide).
• Quicklime: Calcium oxide (CaO), which reacts with water to form slaked lime.
• Limestone: Mainly calcium carbonate (CaCO₃), an important raw material in cement production.
• Carbon dioxide: A colourless, odourless gas produced during respiration, combustion and several industrial processes.
• Greenhouse effect: CO₂ is an important greenhouse gas that absorbs and emits infrared radiation.
• Important distinction: Carbon monoxide (CO) does not produce the characteristic milky limewater test under ordinary conditions.
• Natural occurrence: Carbon dioxide is released by respiration, volcanic activity, decomposition and the burning of carbon-containing fuels.

Quick Revision: CO₂ + Limewater → CaCO₃ (white precipitate) + H₂O → Milky appearance; excess CO₂ → soluble calcium bicarbonate → milkiness disappears.

✔️ Final Answer: (B) CO₂

🚗 Incomplete Combustion of Petrol and Diesel

The incomplete burning of petrol and diesel produces carbon monoxide (CO) when the fuel does not receive sufficient oxygen for complete combustion. Carbon monoxide is a colourless, odourless and highly poisonous gas. Therefore, the correct answer is Option (D) Carbon monoxide. Incomplete combustion may also produce soot and unburnt hydrocarbons, depending on the fuel and engine conditions.

🔥 Complete and Incomplete Combustion

Petrol and diesel contain hydrocarbons. When sufficient oxygen is available, complete combustion mainly produces carbon dioxide and water. When oxygen is insufficient or mixing is poor, incomplete combustion can produce carbon monoxide and other products.

⚗️ Chemical Equations

Complete combustion of carbon:

C + O₂ → CO₂

Incomplete combustion of carbon:

2C + O₂ → 2CO

These simplified equations show why limited oxygen can produce carbon monoxide instead of carbon dioxide. Actual petrol and diesel combustion involves many hydrocarbon reactions inside an engine.

☠️ Why Is Carbon Monoxide Dangerous?

Carbon monoxide is dangerous because it binds strongly with haemoglobin in red blood cells to form carboxyhaemoglobin. This reduces the blood’s ability to transport oxygen to body tissues and can cause serious poisoning.

• Nature: Colourless, odourless and tasteless gas.
• Source: Incomplete combustion of petrol, diesel, coal, wood and other carbon-containing fuels.
• Effect on blood: Combines with haemoglobin to form carboxyhaemoglobin.
• Symptoms: Headache, dizziness, weakness, nausea, confusion and, in severe cases, unconsciousness or death.
• Prevention: Ensure proper ventilation, maintain vehicle engines and never run an engine in a closed garage.

🌫️ Other Important Vehicle Emissions

🧠 Further Exam-Oriented Facts

• Carbon monoxide formula: CO; it is produced when carbon-containing fuels burn with insufficient oxygen.
• Carbon dioxide formula: CO₂; it is the major carbon-containing product of complete combustion.
• Carboxyhaemoglobin: The compound formed when carbon monoxide binds with haemoglobin.
• Catalytic converter: A vehicle emission-control device that helps convert carbon monoxide and unburnt hydrocarbons into less harmful products and reduces nitrogen oxides.
• Diesel particulate filter (DPF): A device designed to trap particulate matter from diesel exhaust.
• Photochemical smog: Forms when nitrogen oxides and volatile organic compounds react in sunlight, producing ground-level ozone and other oxidants.
• Important distinction: Carbon monoxide is mainly associated with incomplete combustion, whereas carbon dioxide is the principal carbon product of complete combustion.

Quick Revision: Insufficient oxygen → Incomplete combustion → CO; sufficient oxygen → Complete combustion → CO₂ + H₂O; CO + haemoglobin → Carboxyhaemoglobin.

✔️ Final Answer: (D) Carbon monoxide

🧪 pH Scale and Hydrogen Ion Concentration

The pH scale measures how acidic or alkaline a solution is. It is defined as the negative logarithm (base 10) of hydrogen ion activity; in elementary calculations, hydrogen ion concentration is commonly used as an approximation. The relationship is expressed as pH = −log₁₀[H⁺]. Therefore, an increase of one pH unit represents a tenfold decrease in hydrogen ion concentration.

In this question, the pH changes from 3 to 6, which is an increase of 3 units. Hence:

Initial concentration: [H⁺] = 10⁻³ mol/L

Final concentration: [H⁺] = 10⁻⁶ mol/L

Ratio: 10⁻³ ÷ 10⁻⁶ = 10³ = 1000

Thus, the hydrogen ion concentration becomes 1/1000 of its initial value, meaning it decreases 1000 times. Therefore, option (D) is correct.

📊 Important pH Values

🧠 Further Exam-Oriented Facts

• Acidic solution: At 25°C, a solution with pH below 7 is acidic.
• Neutral solution: At 25°C, pure water has pH approximately 7.
• Alkaline solution: At 25°C, a solution with pH above 7 is alkaline or basic.
• Logarithmic scale: A change of one pH unit corresponds to a tenfold change in hydrogen ion activity, not a simple one-unit change in acidity.
• Strong acids: Hydrochloric acid (HCl) and nitric acid (HNO₃) are common examples of strong acids.
• Strong bases: Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are common examples of strong bases.
• Biological importance: Human blood normally has a pH of approximately 7.35–7.45. Significant deviation can disturb normal body functions.
• Environmental importance: Acid rain is generally associated with rainwater having a pH below approximately 5.6, mainly due to dissolved sulphur dioxide and nitrogen oxides and the acids they form.

Quick Revision: pH = −log₁₀[H⁺]; pH increases → H⁺ concentration decreases; a rise of 3 pH units → 10³ = 1000-fold decrease.

✔️ Final Answer: (D) Decrease 1000 times

🔥 Sublimation: Separation of Sand and Naphthalene

A mixture of sand and naphthalene can be separated by sublimation because naphthalene changes directly from the solid state into vapour on heating, without passing through the liquid state under ordinary conditions. Sand does not sublime at the temperature used in this experiment and remains behind. On cooling, naphthalene vapour changes directly into solid crystals, allowing it to be collected separately.

🔬 How Does the Separation Work?

• Step 1: Place the mixture of sand and naphthalene in a suitable evaporating dish.
• Step 2: Cover the dish with an inverted funnel, closing the funnel stem with a small cotton plug.
• Step 3: Heat the mixture gently. Naphthalene changes directly into vapour.
• Step 4: The vapour touches the cooler inner surface of the funnel and deposits as solid crystals.
• Step 5: Sand remains in the dish, while naphthalene crystals can be collected from the funnel.

🧬 Sigma and Pi Bonds in Benzene (C₆H₆)

Benzene has the molecular formula C₆H₆ and consists of a six-membered carbon ring. Each carbon atom is bonded to two neighbouring carbon atoms and one hydrogen atom. Therefore, the molecule contains 6 carbon–carbon sigma (σ) bonds and 6 carbon–hydrogen sigma (σ) bonds, giving a total of 12 sigma bonds.

In the conventional Kekulé representation, benzene has three alternating double bonds. Each double bond contains one sigma bond and one pi (π) bond. Since the six carbon–carbon connections already contribute six sigma bonds, the three double bonds contribute 3 pi bonds. Thus, benzene contains 12 sigma bonds and 3 pi bonds.

🌱 Urea: Chemical Formula and Composition

Urea is an organic compound with the chemical formula CO(NH₂)₂, which can also be written as CH₄N₂O. It contains four elements: carbon (C), hydrogen (H), nitrogen (N) and oxygen (O). Therefore, option (D) is correct. Urea is the principal nitrogen-containing waste product excreted by humans and many other mammals through urine.

The molecular structure of urea consists of one carbonyl group (C=O) attached to two amino groups (–NH₂). It is highly soluble in water and is widely used as a nitrogen fertiliser in agriculture.

🌡️ Thermal Conductivity of Metals

Among the given substances—copper, lead, mercury and zinc—mercury is the poorest conductor of heat. Thermal conductivity measures how effectively a material transfers heat. Mercury is a liquid metal at room temperature and has much lower thermal conductivity than the other three metals listed. Therefore, option (C) is correct.

Copper is an excellent conductor of heat and is widely used in heat exchangers, cookware and electrical applications. Zinc also conducts heat much better than mercury, while lead has a higher thermal conductivity than mercury. The comparison is based on typical values near room temperature.

📊 Approximate Thermal Conductivity

Note: Thermal conductivity values are approximate and vary with temperature, purity and the physical condition of the material. The figures above are representative values near room temperature.

🔥 Why Is Mercury a Poorer Conductor of Heat?

Mercury is a metal, but unlike copper, zinc and lead, it remains liquid at ordinary room temperature. Its thermal conductivity is comparatively low because heat transfer through a liquid metal is less efficient than through the solid metallic structures of the other listed metals. This makes mercury the correct answer in this comparison.

🧠 Further Exam-Oriented Facts

• Best conductor among the listed options: Copper has the highest thermal conductivity among copper, lead, mercury and zinc.
• Mercury: Its chemical symbol is Hg and atomic number is 80. It is the only metal that is liquid at standard room-temperature conditions commonly used in school-level science descriptions.
• Melting point of mercury: Approximately −38.83°C; its boiling point is approximately 356.7°C at standard atmospheric pressure.
• Lead: Its chemical symbol is Pb and atomic number is 82. It is a dense, soft metal and is used in lead-acid batteries and radiation shielding.
• Copper: Its chemical symbol is Cu and atomic number is 29. It is widely used in electrical wiring because of its high electrical and thermal conductivity.
• Zinc: Its chemical symbol is Zn and atomic number is 30. It is widely used for galvanisation of iron and steel to help prevent corrosion.
• Thermal versus electrical conductivity: Many metals conduct both heat and electricity well because of mobile electrons, but the relative values differ from metal to metal.
• Insulators: Materials such as wood, rubber, glass and many plastics generally have much lower thermal conductivity than metals.

📌 Important Distinction

Thermal conductivity refers to the ability to conduct heat, whereas electrical conductivity refers to the ability to conduct electric current. A question about the poorest conductor of heat must be answered using thermal conductivity values, not electrical conductivity values.

Quick Revision: Copper ≈ 400 W/m·K; Zinc ≈ 116 W/m·K; Lead ≈ 35 W/m·K; Mercury ≈ 8.3 W/m·K. Hence, mercury has the lowest thermal conductivity among the given options.

✔️ Final Answer: (C) Mercury

🩸 Vitamin K and Blood Clotting

Vitamin K is essential for normal blood clotting (coagulation). It helps the liver produce functional clotting proteins, particularly prothrombin (Factor II) and Factors VII, IX and X. It also activates the anticoagulant proteins C and S. Without sufficient vitamin K, the blood takes longer to clot, increasing the risk of excessive bleeding.

🔬 How Does Vitamin K Work?

Vitamin K acts as a cofactor for an enzyme that carries out gamma-carboxylation of specific glutamate residues in clotting proteins. This modification enables these proteins to bind calcium ions and participate effectively in the coagulation process. The liver is the principal organ responsible for producing most blood-clotting factors.

📊 Types, Sources and Functions of Vitamin K

🧠 Other Important Facts About Vitamins

• Vitamin A: Important for vision, healthy skin, growth and immunity. Deficiency may cause night blindness.
• Vitamin B-complex: A group of water-soluble vitamins involved in energy metabolism, nerve function and red blood cell formation.
• Vitamin C: Necessary for collagen formation, wound healing and iron absorption. Deficiency causes scurvy.
• Vitamin D: Helps calcium and phosphorus absorption and supports healthy bones. Deficiency in children may cause rickets.
• Vitamin E: Acts as an antioxidant and protects cell membranes from oxidative damage.
• Vitamin K deficiency: Can cause prolonged clotting time and bleeding. Newborn babies are particularly vulnerable because they have low vitamin K stores.

🏥 Medical and Examination Facts

• Vitamin K is commonly administered to newborn babies to prevent vitamin K deficiency bleeding.
• Warfarin is an anticoagulant medicine that works by interfering with vitamin K recycling.
• Patients taking warfarin are generally advised to maintain a consistent intake of vitamin K rather than suddenly changing their consumption.
• PT/INR: Prothrombin time and International Normalized Ratio are important tests used to assess blood clotting, particularly in patients taking warfarin.
• Vitamin K is a fat-soluble vitamin, along with vitamins A, D and E.

Quick Revision: Vitamin K → blood clotting; Vitamin C → scurvy prevention; Vitamin D → bones; Vitamin A → vision; Vitamin E → antioxidant.

✔️ Final Answer: (D) vitamin K

♀️ Estrogen: A Major Female Sex Hormone

Estrogen is a major female sex hormone responsible for the development and regulation of the female reproductive system and secondary sexual characteristics. It is produced mainly by the ovaries, particularly by developing ovarian follicles. Smaller quantities are also produced by the placenta during pregnancy and by other tissues, including adipose tissue.

🧬 Major Types of Estrogen

🌸 Functions of Estrogen

• Promotes the development of female reproductive organs and secondary sexual characteristics, including breast development.
• Helps regulate the menstrual cycle and the growth of the uterine endometrium.
• Contributes to the maintenance of bone density and helps reduce excessive bone loss.
• Influences the distribution of body fat and several metabolic processes.
• Participates in the regulation of the hypothalamus and pituitary gland through feedback mechanisms.

📊 Important Hormones and Their Functions

🧠 Further Exam-Oriented Facts

• Progesterone: Another major female reproductive hormone, produced mainly by the corpus luteum and, during pregnancy, by the placenta.
• Androgens: A group of hormones that includes testosterone. They are present in both males and females, although their levels differ.
• Ovaries: Female gonads that produce ova and secrete estrogen and progesterone.
• Testes: Male gonads that produce sperm and secrete testosterone.
• Menopause: The permanent cessation of menstruation due to the loss of ovarian follicular activity, usually occurring in middle age.
• Important distinction: Estrogen is not the only female hormone. Progesterone, FSH and LH also play essential roles in female reproductive physiology.

Quick Revision: Estrogen → female reproductive development; Progesterone → pregnancy support; Testosterone → major androgen; Insulin → blood glucose regulation; Oxytocin → uterine contractions and milk ejection.

✔️ Final Answer: (A) estrogen

🧠 Arvid Carlsson and Parkinson’s Disease

Arvid Carlsson, a Swedish pharmacologist, shared the 2000 Nobel Prize in Physiology or Medicine with Paul Greengard and Eric Kandel. The award recognised their discoveries concerning signal transduction in the nervous system. Carlsson’s research established the important role of dopamine as a neurotransmitter in the brain and helped provide the scientific foundation for dopamine-based treatment of Parkinson’s disease.

🔬 What Is Parkinson’s Disease?

Parkinson’s disease is a progressive neurodegenerative disorder that primarily affects movement. It is associated with the degeneration of dopamine-producing neurons in a region of the brain called the substantia nigra pars compacta, which is part of the basal ganglia system. Reduced dopamine disrupts the normal control of movement and produces characteristic motor symptoms.

⚕️ Role of Dopamine and Levodopa

Dopamine is a neurotransmitter that helps regulate movement, motivation and several other brain functions. Since dopamine itself does not cross the blood-brain barrier effectively, the precursor levodopa (L-DOPA) is used as a medicine. It can enter the brain and be converted into dopamine. Levodopa is commonly administered with carbidopa, which reduces its conversion into dopamine outside the brain and helps improve its availability in the central nervous system.

📊 Important Facts About Parkinson’s Disease

🏅 Nobel Prize: The Other Scientists in the Question

• Arvid Carlsson: Shared the 2000 Nobel Prize in Physiology or Medicine for discoveries concerning signal transduction in the nervous system.
• John F. Enders: Shared the 1954 Nobel Prize in Physiology or Medicine with Thomas H. Weller and Frederick C. Robbins for discoveries relating to the ability of poliomyelitis viruses to grow in cultures of different types of tissue.
• Robert B. Laughlin: Shared the 1998 Nobel Prize in Physics for the discovery of a new form of quantum fluid with fractionally charged excitations.
• Walter Kohn: Shared the 1998 Nobel Prize in Chemistry with John A. Pople for their development of density-functional theory and computational methods in quantum chemistry.

🧠 Further Exam-Oriented Facts

• World Parkinson’s Day: Observed every year on 11 April, the birth anniversary of James Parkinson.
• James Parkinson: Published An Essay on the Shaking Palsy in 1817, describing the condition later known as Parkinson’s disease.
• Substantia nigra: A darkly pigmented region of the midbrain; its dopamine-producing neurons are significantly affected in Parkinson’s disease.
• Deep Brain Stimulation (DBS): A surgical treatment option for selected patients whose symptoms are not adequately controlled by medication.
• Important distinction: Levodopa can improve symptoms, but it is not a cure for Parkinson’s disease. Treatment is individualised and may include medicines, physiotherapy and other supportive care.

Quick Revision: Arvid Carlsson → 2000 Nobel Prize in Physiology or Medicine → dopamine → Parkinson’s treatment foundation → levodopa.

✔️ Final Answer: (A) Arvid Carlsson

🦋 Iodine and the Thyroid Gland

Iodine is an essential trace element required by the thyroid gland to synthesise thyroid hormones. The two principal thyroid hormones are thyroxine (T4) and triiodothyronine (T3). Iodine deficiency can reduce hormone production and may cause thyroid enlargement, known as goitre. Severe deficiency during pregnancy and early childhood can impair normal brain development and physical growth.

🔬 How Does the Thyroid Gland Work?

The thyroid is a butterfly-shaped endocrine gland situated in the front of the neck, below the larynx. It absorbs iodine from the blood and uses it to produce T3 and T4. These hormones regulate the body’s metabolic rate, energy use, body temperature, growth and development. Their secretion is controlled mainly by thyroid-stimulating hormone (TSH), released by the anterior pituitary gland.

📊 Important Thyroid Hormones and Their Functions

⚠️ Disorders Associated with Thyroid Function

• Goitre: Enlargement of the thyroid gland; iodine deficiency is one important cause, although several other conditions can also cause it.
• Hypothyroidism: A condition in which the thyroid gland does not produce sufficient thyroid hormones. Symptoms may include fatigue, weight gain, cold intolerance and slow heart rate.
• Hyperthyroidism: A condition in which the thyroid produces excessive hormones. Symptoms may include weight loss, heat intolerance, sweating and rapid heartbeat.
• Congenital hypothyroidism: Thyroid hormone deficiency present at birth; early diagnosis and treatment are important for normal brain development.
• Autoimmune thyroid disease: Hashimoto’s thyroiditis commonly causes hypothyroidism, whereas Graves’ disease commonly causes hyperthyroidism.

🥗 Sources of Iodine and Prevention

• Iodised salt: An important public-health measure for preventing iodine deficiency disorders.
• Seafood: Fish and other marine foods can provide iodine.
• Dairy products: Milk and some dairy foods contribute to dietary iodine intake.
• Seaweed: Can contain high amounts of iodine, but its iodine content varies considerably.
• Important caution: Excessive iodine intake can also disturb thyroid function. Iodine supplements should not be taken unnecessarily.

🧠 Further Exam-Oriented Facts

• The thyroid gland is located in the neck, while the pituitary gland is situated at the base of the brain.
• Thyroid hormones contain iodine: T3 has three iodine atoms and T4 has four iodine atoms.
• The National Iodine Deficiency Disorders Control Programme (NIDDCP) in India aims to control and prevent iodine deficiency disorders.
• TSH testing, often along with free T4, is commonly used to assess thyroid function.
• Important distinction: Iodine deficiency is a recognised cause of thyroid dysfunction, but not every thyroid disorder is caused by iodine deficiency.

Quick Revision: Iodine → synthesis of T3 and T4; TSH → stimulates thyroid; iodine deficiency → possible goitre and hypothyroidism; Hashimoto’s → commonly hypothyroidism; Graves’ disease → commonly hyperthyroidism.

✔️ Final Answer: (C) iodine

👅 Taste Sensation and the Human Tongue

The expected textbook answer is the posterior part (back) of the tongue for bitterness. Traditional diagrams often show bitterness at the back, sweetness at the tip, sourness along the sides and saltiness near the front sides. However, modern scientific research has established that this traditional tongue map is misleading. Taste receptors for all five basic tastes are distributed across several regions of the tongue and other parts of the oral cavity.

🔬 The Five Basic Tastes

🧬 How Do We Detect Taste?

Taste is detected by specialised sensory cells present in taste buds. Most taste buds are located in structures called papillae on the tongue. When food chemicals dissolve in saliva, they interact with taste receptors or ion channels on these sensory cells. The resulting signals travel through cranial nerves to the brain, where taste information is processed.

📊 Important Types of Tongue Papillae

🧠 Further Exam-Oriented Facts

• Five basic tastes: Sweet, salty, sour, bitter and umami.
• Umami: A savoury taste commonly associated with glutamate, found naturally in foods such as tomatoes, mushrooms and some fermented products.
• Taste buds: Microscopic sensory structures containing specialised taste receptor cells.
• Saliva: Helps dissolve food chemicals so that they can interact with taste receptors.
• Smell and taste: Flavour is produced by the combined contribution of taste, smell, texture and other sensory signals. This is why food may seem less flavourful during a cold.
• Important scientific correction: The entire tongue is not equally sensitive to every taste in every circumstance, but there are no sharply separated zones exclusively responsible for individual tastes.

Quick Revision: Traditional exam answer for bitterness → posterior part of tongue; modern science → taste receptors for all five basic tastes occur across multiple regions; five tastes → sweet, salty, sour, bitter and umami.

✔️ Final Answer: (C) posterior part

🏃 Fit India Movement and Its Fitness Mantra

On 24 September 2020, on the occasion of the first anniversary of the Fit India Movement, Prime Minister Narendra Modi gave the fitness mantra “Fitness Ki Dose, Aadha Ghanta Roz”, encouraging people to devote at least 30 minutes every day to physical fitness. He announced this during the Fit India Dialogue, an interaction with sportspersons, fitness experts and other personalities. The message emphasized that regular physical activity should become an integral part of everyday life.

📅 Important Facts about the Fit India Movement

• Launch date: 29 August 2019.
• Launched by: Prime Minister Narendra Modi.
• Occasion: National Sports Day, observed on the birth anniversary of hockey legend Major Dhyan Chand.
• First anniversary: 29 August 2020 marked the first anniversary of the movement; the Fit India Dialogue and the launch of age-appropriate fitness protocols took place on 24 September 2020.
• Main objective: To make fitness an integral part of the daily lives of citizens and encourage behavioural change towards a healthy lifestyle.
• Fitness mantra: “Fitness Ki Dose, Aadha Ghanta Roz” — at least half an hour of physical activity every day.

📊 Age-Appropriate Fitness Protocols

On 24 September 2020, the Prime Minister also launched age-appropriate fitness protocols under the Fit India initiative. These protocols were designed for different age groups so that physical activity could be adapted to people’s age and fitness levels.

🏅 Other Important Initiatives Related to Fitness

• Fit India School Week: An initiative to encourage schools to make physical activity and fitness part of students’ daily routines.
• Fit India Freedom Run: A nationwide initiative encouraging people to run or undertake physical activities according to their ability.
• Fit India Mobile App: Provides fitness-related features, including fitness scores, activity tracking and age-appropriate fitness guidance.
• Fit India Movement: It is a nationwide people’s movement rather than merely a sports competition or a government fitness programme.
• WHO recognition: The World Health Organization appreciated India’s campaign promoting physical activity through the message “Fitness Ki Dose, Aadha Ghanta Roz”.

🧠 Important Exam-Oriented Facts

• 29 August: National Sports Day in India.
• Major Dhyan Chand: Legendary Indian hockey player, popularly known as the Wizard of Hockey.
• Fit India Movement: Launched on 29 August 2019.
• Fit India Dialogue: Held on 24 September 2020 on the occasion of the movement’s first anniversary celebrations.
• GOALS: The age-appropriate fitness protocols were associated with the concept of Goals for Active Life Style.
• Daily fitness message: At least 30 minutes of physical activity every day.

Quick Revision: Fit India Movement → 29 August 2019 → Prime Minister Narendra Modi → First-anniversary Fit India Dialogue → 24 September 2020 → “Fitness Ki Dose, Aadha Ghanta Roz”.

✔️ Final Answer: (A) Prime Minister Narendra Modi

🪙 Commemorative Coin in Honour of Rajmata Vijaya Raje Scindia

On 12 October 2020, Prime Minister Narendra Modi released a special commemorative coin of ₹100 denomination to mark the birth centenary of Rajmata Vijaya Raje Scindia. The coin was released through a virtual ceremony. The date was also her birth anniversary. The commemorative coin was minted by the Ministry of Finance as part of the birth-centenary celebrations. Therefore, the correct answer is a one hundred rupees coin, not a currency note.

👑 Who Was Rajmata Vijaya Raje Scindia?

Rajmata Vijaya Raje Scindia (12 October 1919 – 25 January 2001) was a prominent Indian political leader and a member of the former royal family of Gwalior. She was popularly known as the Rajmata of Gwalior. She played an important role in Indian politics, particularly in the development of the Bharatiya Jana Sangh and later the Bharatiya Janata Party (BJP).

• Birth: 12 October 1919.
• Birthplace: Sagar, in present-day Madhya Pradesh.
• Popular title: Rajmata of Gwalior.
• Political association: Bharatiya Jana Sangh and Bharatiya Janata Party.
• Death: 25 January 2001.
• Birth centenary: 12 October 2019 marked 100 years since her birth.
• Commemorative coin released: 12 October 2020, by Prime Minister Narendra Modi.

📊 Important Details of the Commemorative Coin

🪙 Commemorative Coins: Important Concepts

• Commemorative coin: A coin issued to honour a notable person, event, institution or important national occasion.
• Denomination: The face value assigned to a coin or currency note, such as ₹10, ₹50 or ₹100.
• Coin versus currency note: The ₹100 issued in honour of Rajmata Vijaya Raje Scindia was a coin, not a ₹100 banknote.
• Ministry of Finance: The commemorative coin was minted under the authority of the Ministry of Finance.
• Historical importance: Commemorative coins preserve the memory of important personalities and events through currency-related national symbols.

🧠 Further Exam-Oriented Facts

• Gwalior: Rajmata Vijaya Raje Scindia was closely associated with the former princely state of Gwalior.
• Political contribution: She was an influential leader associated with the Bharatiya Jana Sangh and the BJP.
• Birth centenary: A centenary marks the completion of 100 years.
• Important date distinction: Her 100th birth anniversary fell on 12 October 2019, while the commemorative coin was released on 12 October 2020.
• Exam point: The question asks what was released, not the year in which the birth centenary itself was completed.

Quick Revision: Rajmata Vijaya Raje Scindia → Born 12 October 1919 → Birth centenary in 2019 → ₹100 commemorative coin released by PM Narendra Modi on 12 October 2020.

✔️ Final Answer: (C) one hundred rupees coin

🎬 “Chi Lupo” — An Award-Winning Documentary from Arunachal Pradesh

The short documentary film “Chi Lupo”, associated with Arunachal Pradesh, won the Best Documentary Award at the Dadasaheb Phalke Film Festival–2020. The film depicts the traditional honey-hunting practices of the Sherdukpen community of West Kameng district in Arunachal Pradesh. It was directed by independent filmmaker Kezang D. Thongdok. The award was announced in April 2020, and the film brought attention to the traditional knowledge, culture and livelihood practices of a tribal community in the state.

🍯 What Does “Chi Lupo” Mean?

• Chi: Honey.
• Lupo: Hunter.
• Meaning: “Honey Hunter” or a person engaged in honey hunting.
• Subject: Traditional honey hunting among the Sherdukpen community.
• Location: West Kameng district, Arunachal Pradesh.
• Director: Kezang D. Thongdok.
• Award: Best Documentary at the Dadasaheb Phalke Film Festival–2020.

🏞️ The Sherdukpen Community

The Sherdukpen are an indigenous community of Arunachal Pradesh, mainly associated with the Rupa and Shergaon areas of West Kameng district. Their traditional practices, festivals, language and knowledge of the natural environment form an important part of the cultural diversity of the state. Honey hunting is one of the traditional activities documented in the film.

📊 Important Facts about the Documentary

🎥 Dadasaheb Phalke: Important Facts

• Dadasaheb Phalke: Widely regarded as the Father of Indian Cinema.
• First Indian feature film: Raja Harishchandra (1913), directed by Dadasaheb Phalke.
• Dadasaheb Phalke Award: India’s highest award in the field of cinema, instituted in 1969.
• First recipient: Devika Rani received the first Dadasaheb Phalke Award in 1969.
• Important distinction: The Dadasaheb Phalke Award presented by the Government of India is a national lifetime-achievement honour. The Dadasaheb Phalke Film Festival is a separate film festival with its own award categories. The “Chi Lupo” recognition in this question refers to the film festival award.

🌏 Additional Exam-Oriented Facts about Arunachal Pradesh

• Capital: Itanagar.
• Statehood: Arunachal Pradesh became a full-fledged state on 20 February 1987.
• Largest town: Itanagar is the state capital and an important urban centre.
• Geographical position: It is located in the northeastern part of India and shares international borders with Bhutan, China and Myanmar.
• Major river: The Siang, which is known as the Brahmaputra after entering Assam, is an important river system of the region.
• West Kameng: The district is associated with the Sherdukpen community and the traditional practices shown in “Chi Lupo”.

Quick Revision: “Chi Lupo” → Honey hunting → Sherdukpen community → West Kameng → Arunachal Pradesh → Kezang D. Thongdok → Dadasaheb Phalke Film Festival–2020.

✔️ Final Answer: (D) Arunachal Pradesh

🌾 HDFC Bank’s “e-Kisaan Dhan” App

HDFC Bank launched the “e-Kisaan Dhan” mobile application for farmers on 30 June 2020. The app was designed as a one-stop digital platform to provide agricultural information and banking services to people engaged in farming. It aimed to bridge the information gap in the rural agricultural ecosystem by making useful information and financial services accessible through mobile phones. The initiative was associated with the bank’s “Har Gaon Hamara” programme.

📱 Major Features of the e-Kisaan Dhan App

The application brought together agricultural information, advisory services and banking facilities. Its important features included:

• Mandi prices: Information about agricultural commodity prices in mandis.
• Weather forecasts: Weather-related information to help farmers plan agricultural activities.
• Farming news: Latest news and updates related to agriculture.
• Seed information: Information about different varieties of seeds.
• SMS advisory: Agricultural guidance and useful messages for farmers.
• e-Pashuhaat: Access to information and services related to livestock and animal husbandry.
• Kisan TV: Agricultural knowledge and educational content for farmers.
• Banking services: Access to banking facilities, loans, insurance-related services and government social security schemes.

📊 Important Details about the App

🏦 HDFC Bank: Important Banking Facts

• Full name: Housing Development Finance Corporation Bank (HDFC Bank).
• Established: 1994.
• Headquarters: Mumbai, Maharashtra.
• Banking category: Private sector bank.
• Banking operations: HDFC Bank commenced operations in January 1995.
• RBI connection: HDFC Bank was among the first private sector banks to receive approval from the Reserve Bank of India under the liberalisation policy of the 1990s.
• Merger: HDFC Ltd., the housing finance company, merged with HDFC Bank with effect from 1 July 2023. This was an important development in India’s financial sector.

🌱 Digital Banking and Agriculture

Digital platforms can improve farmers’ access to financial services and agricultural information. Mobile-based services can help farmers obtain market-price information, weather updates, agricultural advisories and banking facilities without depending entirely on physical branches or intermediaries.

• Financial inclusion: Expanding access to affordable financial services for individuals and businesses that are underserved by the formal financial system.
• Digital banking: Delivery of banking services through digital channels such as mobile applications and internet banking.
• Agri-finance: Financial services designed for agricultural activities, including crop loans, equipment finance and insurance.
• e-NAM: National Agriculture Market, an electronic trading portal intended to create a more integrated national market for agricultural commodities.
• Kisan Credit Card (KCC): A credit facility intended to provide timely and adequate credit support to farmers for agricultural and related activities.

🧠 Important Exam-Oriented Facts

• e-Kisaan Dhan: HDFC Bank.
• Launch date: 30 June 2020.
• Associated programme: Har Gaon Hamara.
• e-NAM: An electronic platform for agricultural marketing.
• KCC: Kisan Credit Card, a credit facility for farmers.
• Important distinction: e-Kisaan Dhan was a banking-sector mobile application, whereas e-NAM is a national electronic agricultural marketing platform.

Quick Revision: e-Kisaan Dhan → HDFC Bank → 30 June 2020 → Farmers → Agricultural information + banking services → Har Gaon Hamara initiative.

✔️ Final Answer: (B) HDFC Bank

🦠 India’s First Airport COVID-19 Testing Facility — Delhi

India’s first airport-based COVID-19 testing facility was launched at the Indira Gandhi International Airport (IGI), Delhi, in September 2020. The facility was established at Terminal 3 of the airport and began operations on 13 September 2020. It was set up by Delhi International Airport Limited (DIAL) in collaboration with Genestrings Diagnostic Centre. The facility was intended to help arriving international passengers, particularly those who needed to take connecting domestic flights, obtain COVID-19 test results at the airport.

📍 Important Details of the Facility

🔬 What Is RT-PCR Testing?

RT-PCR stands for Reverse Transcription Polymerase Chain Reaction. It is a molecular diagnostic technique used to detect the genetic material of RNA viruses, including SARS-CoV-2, the virus responsible for COVID-19.

• Sample: During the COVID-19 pandemic, samples were commonly collected using nasopharyngeal or oropharyngeal swabs.
• Reverse transcription: Viral RNA is converted into complementary DNA (cDNA).
• Polymerase Chain Reaction: Specific genetic sequences are amplified so that they can be detected.
• Result: Detection of the targeted viral genetic material indicates the presence of the virus in the collected sample.
• Importance: RT-PCR was widely used as a molecular diagnostic method for COVID-19 testing.

✈️ COVID-19 Screening at Indian Airports: Important Distinction

India began screening international passengers for COVID-19 symptoms at selected airports in January 2020, before the airport-based testing laboratory was launched in Delhi in September 2020. These were two different measures: initial airport screening involved checking passengers for symptoms, whereas the September facility provided laboratory-based COVID-19 testing.

🧪 Important COVID-19 and Health Facts

• COVID-19: An infectious disease caused by the SARS-CoV-2 virus.
• WHO pandemic declaration: The World Health Organization characterized COVID-19 as a pandemic on 11 March 2020.
• First reported cases: The outbreak was initially identified in Wuhan, China, in December 2019.
• RT-PCR: A molecular method used to detect viral genetic material.
• ICMR: Indian Council of Medical Research, India’s apex body for the formulation, coordination and promotion of biomedical research.
• NABL: National Accreditation Board for Testing and Calibration Laboratories, which provides accreditation to testing and calibration laboratories.
• Airport screening versus testing: Thermal screening checks for indicators such as elevated body temperature; a laboratory test such as RT-PCR detects specific viral genetic material.

🧠 Further Exam-Oriented Facts

• IGI Airport: Located in Delhi and named after former Prime Minister Indira Gandhi.
• Airport code: DEL.
• Terminal 3: The terminal where India’s first airport-based COVID-19 testing facility was established.
• DIAL: Delhi International Airport Limited, the airport operator involved in setting up the facility.
• Important distinction: The first airport-based COVID-19 testing facility in India was in Delhi, while the initial thermal screening of international passengers had started at multiple airports in January 2020.

Quick Revision: First airport-based COVID-19 testing facility → Delhi → Indira Gandhi International Airport → Terminal 3 → September 2020 → DIAL + Genestrings Diagnostic Centre → RT-PCR.

✔️ Final Answer: (B) Delhi