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Environmental Governance — UPSC Prelims Science & Environment previous year questions

149 solved previous year questions on Environmental Governance, papers from 1994 to 2023, drawn from UPSC CSE Prelims, UPPCS, UPSC CDS. Each carries the printed answer key and the explanation from the source compilation.

1. #1UPSC CSE Prelims 2013
   Ball bearings are used in bicycles, cars, etc., because
   • Athe actual area of contact between the wheel and axle is increased
   • Bthe effective area of contact between the wheel and axle is increased
   • Cthe effective area of contact between the wheel and axle is reduced
   • DNone of the above statements is correct
   Answer: (C) the effective area of contact between the wheel and axle is reduced
   Explanation

   Option c is the correct ball bearing is a type of rolling-element bearing that main functions while it facilitates motion: it reduces friction and positions moving machine bearings are used in bicycles, cars, etc., because area of contact between the wheel and axle this reduces friction

2. #2Previous year
   Consider the following minerals:40. 1. Calcium 2. Iron 3. SodiumWhich of the minerals given above is/ are required by the human body for the contraction of muscles? [UPSC CSE Pre 2013)
   • A1 only
   • B2 and 3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (D) 1, 2 and 3
   Explanation

   Option dis the correct three minerals mentioned-calcium, iron, required by the human body for of muscle function: Calcium: Calcium plays a fundamental role in muscle contraction. It is released from the sarcoplasmic reticulum within muscle cells, enabling the interaction between actin and myosin filaments, leading to muscle contraction. Iron: Iron is essential for muscle function indirectly. It is a critical component of hemoglobin, which transports oxygen from the lungs to muscles. Adequate oxygen supply is vital for energy production during Sodium ions are involved in the transmission signals to muscles, initiating muscle also participate in maintaining the electrical cell membranes, which is crucial for muscle function

3. #3UPSC CSE Prelims 2013
   Consider the following animals: 1. Sea cow 2. Seahorse 3. Sea lionWhich of the above is/are mammal/ mammals?
   • A1 only
   • B1 and 3 only
   • C2 and 3 only
   • DAll of these
   Answer: (B) 1 and 3 only
   Explanation

   Option bis the correct cows and sea lions are mammals. Seahorses are are a class of vertebrates that are characterized fur or hair, mammary glands, and three middle They also give birth to live young and nurse them Fish are a class of vertebrates that are characterized gills, fins, and scales. They also lay NOLOGY The Sil'enia, commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Sea lions are also large, carnivorous marine mammals. They are found in coastal waters around the world. Seahorses are small, bony fish that are found in coastal waters around the world. They are known for their unique male pregnancy, in which the male seahorse carries the eggs in a pouch on its abdomen

4. #4Previous year
   The function of heavy water in a nuclear reactor is to [UPSC CSE Pre
   • ASlow down the speed of neutrons
   • BIncrease the speed of neutrons
   • CCool down the reactor
   • DStop the nuclear reaction
   Answer: (A) Slow down the speed of neutrons
   Explanation

   Option a is the correct is required in a Nuclear reactor to slow neutrons produced during the fission reaction so chain reaction can be sustained. Heavy Water is moderator due to its high moderating ratio and cross section for neutrons

5. #5UPSC CSE Prelims 2011
   A layer in the Earth's atmosphere called Ionosphere facilitates radio communication. Why? 1. The presence of ozone causes the reflection of radio waves to Earth. 2. Radio waves have a very long wavelength.Which of the statements given above is/are correct?
   • A1 only
   • B2 only
   • CBoth 1 and 2
   • DNeither 1 nor 2 T
   Answer: (D) Neither 1 nor 2 T
   Explanation

   Option d is the correct 1 is incorrect- The ionosphere is a layer of atmosphere that is ionized by soiar radiation. that the atoms and molecules in the lost some of their electrons. The free electrons ionosphere reflect radio waves, is,vhy facilitates radio communication. Ozone is that is found in the stratosphere, a layer of the that is located above the ionosphere. not reflect radio 2 is incorrect- Radio waves can have a of wavelengths. Some radio waves, such as AM have very long wavelengths, while others, such radiation, have very short wavelengths. of a radio wave does not affect whether or not reflected by the ionosphere

6. #6Previous year
   Consider the following: 1. Camphor 2. Chicory 3. VanillaWhich of the above is/are plant [UPSC CSE Pre 2009)
   • A1 and 2 only
   • B3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (D) 1, 2 and 3
   Explanation

   Option d is the correct 1 is correct- Camphor is a plant product. a waxy, white solid that is extracted from the bark of the camphor laurel tree. It is used in a variety including liniments, ointments, and cough 2 is correct- Chicory is a plant product. Chicory is plant that is native to Europe and Asia. It is a food crop and as a coffee substitute. Chicory root roasted and ground to make a coffee-like 3 is correct- Vanilla is a plant product. Vanilla is that is extracted from vanilla orchid. It is used in of food and beverage products, including ice and baked goods

7. #7Previous year
   Consider the following statements about probiotic food: 1. Probiotic food contains live bacteria which are considered beneficial to humans. 2. Probiotic food helps in maintaining gut flora.Which of the statements given above is/are correct? [UPSC CSE Pre 2008)
   • A1 only
   • B2 only
   • CBoth 1 and 2
   • DNeither nor 2
   Answer: (C) Both 1 and 2
   Explanation

   Option c is the correct l is correct: Probiotic food contains live as Lactobacillus and Bifidobacterium strains, which beneficial to 2 is correct: Probiotic food helps maintain gut flora by introducing beneficial live the digestive system. These bacteria colonize the contribute to a balanced microbial environment. outcompete harmful microbes, support produce compounds that promote gut health. of gut flora can lead to improved absorption, and potentially enhance overall well being

8. #8UPSC CSE Prelims 2008
   Which one of the following is an insectivorous plant?
   • APassionflower plant
   • BPitcher plant
   • CNight queen
   • DFlame of the forest
   Answer: (B) Pitcher plant
   Explanation

   Option b is the correct plants are insectivorous plants known for pitcher-shaped leaves that act as deadly traps They lure insects into their tubular leaves and colorful markings. Once inside, the trapped and are eventually digested by the The digestive process transforms the prey valuable nutrient solution consisting of amino phosphates, ammonium, and urea. This allows pitcher plants to thrive in soils by acquiring vital minerals, particularly phosphorus. Lid Leaf modified into pitcher Pitcher plant showing lid and pitcher

9. #9Previous year
   Four wires of same material and dimensions as mentioned below are stretched by a load of same magnitude separately. Which one of them will be elongated maximum? [UPSC CSE Pre 2007)
   • AWire of 1 m length and 2 mm diameter
   • BWire of 2 m length and 2 mm diameter
   • CWire of 3 m length and 1.5 mm diameter
   • DWire of 1 m length and 1 mm diameter
   Answer: (C) Wire of 3 m length and 1.5 mm diameter
   Explanation

   Option c is the correct elongation of a wire is given by the following Length) / Young's is the force applied to the is the length of the is the cross-sectional area of the modulus is the modulus of elasticity of the the all four wires are made of the same material and same load applied to them, the elongation of each depend only on its length and wire with the higher value of ratio of length and area will have the greatest elongation. In the wire with the highest value of ratio of length sectional area is the wire of 3 m length and 1.5 the wire of 3 m length and 1.5 mm diameter the maximum

10. #10Previous year
    Which one of the following is the correct sequence in the order decreasing the length of the three structural parts given below, of the small intestine in the human body? [UPSC CSE Pre 2007)
    • AJejunum - Duodenum - Ileum
    • BIleum - Duodenum - Jejunum
    • CJejunum - Ileum - Duodenum
    • DIleum - Jejunum - Duo'denum
    Answer: (D) Ileum - Jejunum - Duo'denum
    Explanation

    Option d is the correct correct sequence in the order of decreasing length three structural parts of the small intestine in the is

11. #11Previous year
    Which one of the following parts of the pitcher plants becomes modified into a pitcher? [UPSC CSE Pre 2007)
    • AStem
    • BLeaf
    • CStipule
    • DPetiole
    Answer: (B) Leaf
    Explanation

    Option b is the correct pitcher of a pitcher plant is a modified leaf. The leaf into a tube and has a lid that covers the opening. is filled with a liquid that attracts and traps an insect falls into the pitcher, it is unable to is eventually digested by the Solution: Option d is the correct insects respire through a system of tubes are tiny tubes that branch insect's body. Ah enters the tracheae through on the insect's sides called Bpiracles. The afr through the tracheae and into the insect's do not have lungs, so they cannot breathe air in way that humans and other animals do. Instead, diffuses directly from the into the insect's system of respiration is very efficient and allows get the oxygen they need even when they are very active. SYSTEM OF Solution: Option d is the correct I is A flute of smaller length of higher frequency. This is because the frequency sound wave is inversely pr

12. #12UPSC CSE Prelims 2005
    Consider the following statements: 1. Liquefied Natural Gas (LNG) is liquefied under extremely cold temperatures and high pressure to facilitate storage or transportation in specially designed vessels. 2. First LNG terminal in India was built in Hassan. 3. Natural Gas Matters (NGM) are separated from LPG, and these include ethane, propane, butane and natural gasoline.Which of the statements given above is/are correct?
    • A1 only
    • B1 and 3 only
    • C2 and 3 only
    • D1, 2 and 3
    Answer: (B) 1 and 3 only
    Explanation

    Option bis the correct l is correct: LNG is natural gas that has down to liquid form for ease and safety of non pressurized storage or transport. The liquefaction the volume of natural gas by about 600 times, more economical to transport across long 2 is incorrect: The first LNG terminal in built in Dahej in Gujarat. It was commissioned in Petronet LNG Limited, a joint venture of four companies. Hassan is a city in Karnataka, which have any L G terminal as of 3 is correct: NGM are natural gas liquids separated from the natural gas before it is pipelines. They include ethane, propane, and natural gasoline. LPG is a type of NGM mainly of propane and butane. NGM are separate products and can be used as fuels, feedstocks, with gasoline

13. #13UPSC CSE Prelims 2005
    Consider the following statements: Assertion (A): The main component of liquefied petroleum gas is methane. Reason Methane can be used directly for burning in homes and factories where it can be supplied through pipelines. Code
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not the correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (D) (A) is false, but (R) is true
    Explanation

    Option d is the correct (A) is false: The main component of gas (LPG) is not methane, but butane and is the main component of compressed natural (R) is true: Methane can be used directly for homes and factories where it can be supplied This is because methane has a high calorific burns with a clean flame

14. #14UPSC CSE Prelims 2003
    Which one of the following statements is correct?
    • ALiquid sodium is employed as a coolant in nuclear reactors
    • BCalcium carbonate is an ingredient of toothpaste
    • CBordeaux mixture consists of sodium sulphate and lime
    • DZinc amalgams are used as a dental filling
    Answer: (B) Calcium carbonate is an ingredient of toothpaste
    Explanation

    Option b is the correct carbonate is an ingredient of toothpaste. is a mild abrasive that helps to remove plaque SCIENC_E from the teeth. It also acts as a filler and a in sodium is highly reactive and can cause fires if it comes in contact with water or mixture consists of copper sulphate and lime. It as a fungicide to prevent fungal diseases on amalgams are not used as a dental filling. Zinc alloys of zinc and other metals, such as mercury, copper. They are used for various purposes, such electrodes, or corrosion protection. Dental usually made of composite resin, porcelain, or Solution: Option c is the correct the hydrogen-inflated polythene balloon rises to in the atmosphere, it will increase in size. balloon rises, the atmospheric pressure decreases, inside the balloon remains relatively constant. the pressure inside the balloon to push the balloon expand. The balloon will expand un

15. #15UPSC CSE Prelims 2002
    Consider the following statements: Assertion (A): Synthetic detergents can make more lather in hard water. Reason Synthetic detergents form soluble calcium and magnesium salts with hard water. Code
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not the correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (A) Both (A) and (R) are true, and (R) is the correct explanation of (A)
    Explanation

    Option a is the correct (A) and (R) are true, and (R) is the correct (A): Synthetic detergents can produce more lather in because they are specifically designed to overcome posed by hard water. Hard water contains magnesium ions, which tend to react with forming insoluble precipitates that reduce detergents, on the other hand, contain can bind to these ions and form soluble complexes and magnesium ions, preventing the formation or soap curd that typically occurs when soap hard water. This property of detergents helps their cleaning efficiency in the presence of Important Tips Difference Between Soap and Detergent Detergents Consist of a '-COONa' Consist of a '-S0 3 Na' group group attached to a fatty attached to a long alkyl acid having a long alkyl chain. chain. They are not effective in They do not lose their hard water and saline water. effectiveness in hard water and saline water. So

16. #16UPSC CSE Prelims 2001
    Two wires have their lengths, diameters and resistivities all in the ratio of l 2. If the resistance of the thinner wire is l O ohm, the resistance of the thicker wire is
    • A5 ohm
    • B10 ohm
    • C20 ohm
    • D40 ohm
    Answer: (B) 10 ohm
    Explanation

    Option b is the correct resistivity of the wire is given by, where p resistance or resistivity (it is a constant), 1 the wire, a area of the cross-section of the d 2 where r radius of the cross-section, d of the R 1 10 Ohms, R2 values, in the formula, l resistance of the thicker wire is 10 ohm

17. #17UPSC CSE Prelims 2001
    Consider the following statements: Assertion (A): A chemical reaction becomes faster at a higher temperature. Reason At higher temperature, molecular motion becomes more rapid. Code: T
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not the correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (A) Both (A) and (R) are true, and (R) is the correct explanation of (A)
    Explanation

    Option a is the correct (A) is true- The rate of a chemical with (R) is true, but (R) is the correct explanation of higher temperatures, the molecules have more and move faster. This means that the molecules likely to collide with each other, which can lead to reaction

18. #18UPSC CSE Prelims 2001
    A radioactive substance has a half-life of four months. Three-fourth of the substance would decay in
    • A3 months
    • B4 months
    • C8 months
    • D12 months
    Answer: (C) 8 months
    Explanation

    Option c is the correct ½ life in 4 In another 4 months - half of remaining ½ decay In 8 months - ½ (½/2) ½ ¼ in a total of 8 months, three-fourths of the decay

19. #19UPSC CSE Prelims 2001
    Consider the following statements:In a nuclear reactor, self-sustained chain reaction is possible, because: 1. More neutrons are released in each of the fission reactions. 2. The neutrons immediately take part in the fission process. 3. The fast neutrons are slowed down by graphite. 4. Every neutron released in the fission reaction initiates further fission.Which of these statements are correct?
    • A1, 2 and 3
    • B1 and 3
    • C2 and 4
    • D2, 3 and 4
    Answer: (B) 1 and 3
    Explanation

    Option bis the correct l is correct- When a fissile nucleus, such absorbs a neutron, it splits into two and releases two or three neutrons. This called nuclear fission. The neutrons released in can then go on to split other fissile nuclei, creating 2 is incorrect- The neutrons released in are fast neutrons. Fast neutrons are less likely fission than slow neutrons. This is because are more likely to escape from the reactor can split a fissile 3 is correct- Graphite is a material that is slow down fast neutrons. This makes it more likely neutrons will split into a fissile nucleus, which helps the chain 4 is incorrect- Not every neutron released in reaction initiates further fission. Some neutrons from the reactor, and others may be absorbed materials in the reactor

20. #20UPSC CSE Prelims 2001
    When light waves pass from air to glass the variable affected are
    • AWavelength, frequency and velocity
    • BVelocity and frequency
    • CWavelength and frequency
    • DWavelength and velocity
    Answer: (D) Wavelength and velocity
    Explanation

    Option d is the correct When light waves pass from air to glass, two variables wavelength and As light enters a denser medium like glass less dense medium like air, its wavelength decreases. is a result of the change in the speed of light media, as described by the equatio where is the wavelength in the medium, is the wavelength and n is the refractive index of the medium. refractive index of glass is greater than that of air, of light in glass is The speed of light in a medium is to its refractive index. Therefore, as light from air, its velocity decreases. This change in a fundamental property of refraction and is described frequency of the light ray remains the same when from one medium to another because it the source of light. But the wavelength and speed they depend on the medium through which the

21. #21Previous year
    When water is heated from to 1000 C. It's volume: [UPSC CSE Pre 2001)
    • AIncreases
    • BDecreases
    • CDoes not change
    • DFirst decreases and then increases
    Answer: (D) First decreases and then increases
    Explanation

    Option d is the correct water is heated from to its a complex change. Initially, as the from to about the volume of water is due to the fact that water reaches its maximum approximately Beyond as water continues it expands and its volume increases. So, the volume first decreases as it warms from to and as it heats further from to Cl) 1.0004 E 1.0003 Q) E.a 0 1.0002 - Q) 1.0001 1.0000 0 2 4 6 8 10 Temperature (0 C)

22. #22UPSC CSE Prelims 2000
    The 'stones' formed in human kidney consist mostly of
    • ACalcium oxalate
    • BSodium acetate
    • CMagnesium sulphate
    • DCalcium
    Answer: (A) Calcium oxalate
    Explanation

    Option a is the correct stones are mostly composed of calcium is a type of salt that forms when calcium and in the urine 1. Kidney stones are solid masses cause severe pain and blockage in the urinary factors that can increase the risk of developing are dehydration, high intake of animal and oxalate-rich foods, obesity, and certain

23. #23UPSC CSE Prelims 2000
    At which stage in its life cyde, does the silkworm yield the fibre of commerce?
    • AEgg
    • BLarva
    • CPupa
    • DImago Formnlm lh
    Answer: (C) Pupa
    Explanation

    Option c is the correct silkworm is a moth that produces silk. The silk is the silkworm's larva, or caterpillar. The larva spins around itself to protect itself while it transforms into pupa. The pupa is the stage of the silkworm's life which silk is produced. The silkworm cocoon is made single strand of silk that is about 3,000 feet long. The produced by the silkworm's silk glands, which are its head. Silk is a liquid when it is first produced, but as it comes into contact with the air. The is harvested, and the silk is unwound from The silk is then spun into thread and woven Silk is a valuable fabric that is used to make and other items. adult moths matewitb each other. The catetpillat spins a silk i _ ) t / ililelf. People the the cocoons to in ilk cloth

24. #24UPSC CSE Prelims 2000
    Consider the following statements:Hard water is not suitable for- 1. Drinking 2. Washing clothes with soap 3. Use in boilers 4. Irrigating cropsWhich of these statements are correct?
    • A1 and 2 only
    • B2 and 3 only
    • C1, 2 and 4 only
    • D1, 2, 3 and 4
    Answer: (D) 1, 2, 3 and 4
    Explanation

    Option d is the correct water is not suitable for drinking, washing soap, use in boilers, or irrigating Hard water contains dissolved minerals, calcium and magnesium. These minerals can make to absorb nutrients from food and can also lead clothes with soap: Hard water can react with form soap scum, which reduces the effectiveness of cleaning. This can make washing clothes in hard water and can leave a residue on in boilers: Hard water can lead to scale buildup and heating systems, reducing their efficiency causing damage over time. Soft water is for use in boilers to prevent these crops: Irrigating crops with hard water can lead buildup of minerals in the soil, potentially affecting and making it difficult for plants to absorb water is often preferred for agricultural purposes these problems. Important Tips Hard Water and Its Types: Hard water is water that contains a high mineral conten

25. #25Previous year
    When a CD (compact disc used in audio and video systems) is seen in sunlight, rainbow like colours are seen. This can be explained on the basis of the phenomenon of [UPSC CSE Pre 2000)
    • AReflection and diffraction
    • BReflection and transmission
    • CDiffraction and transmission
    • DRefraction, diffraction, and transmission
    Answer: (A) Reflection and diffraction
    Explanation

    Option a is the correct rainbow-like colors seen on a CD are due to of reflection and diffraction. The surface CD is covered with a thin layer of metal, which The metal layer is also covered with a series of and lands. The pits are smaller than the lands, and less light. However, some of the light is also the pits and lands. The diffracted light is spread out spectrum of colors, just like a rainbow. The color of that is seen depends on the angle at which the diffracted. The shorter wavelengths of light, such as violet, are diffracted more than the longer wavelengths of light, such as red and orange. This is why the of light are seen at the edge of the CD, while wavelengths of light are seen in the center

26. #26UPSC CSE Prelims 1997
    The most reactive among the halogens is
    • AFluorine
    • BChl or ine
    • CBromine
    • DIodine
    Answer: (A) Fluorine
    Explanation

    Option a is the correct is the most reactive halogen. Halogens are of five elements in the periodic table: bromine, iodine, and astatine. Halogens are because they have seven electrons in their and need one more electron to fill their outer become stable. Fluorine is the most reactive it has the smallest atomic radius and the of the halogens. This means that the strongest attraction for electrons, making it reactive halogen. Chlorine is the next most followed by bromine and iodine. Astatine is reactive halogen, but it is so rare that its properties well known (decreases down the group) n of in an l down Uie group cue to the In energy tevets.. The Nrthet from t h e and M e not.eadlothef. An lnaease: In observed. liernfofe t 0 4.0 M VI Important Tips Physical and Chemical Properties of Halogens: Halogens are a group of elements located in Group 17 of the periodic table which includes fluor

27. #27UPSC CSE Prelims 1997
    A girl is swinging on a swing in a sitting position. When the girl stands up, the period of the swing will
    • ABe shorter
    • BBe longer
    • CDepends on the height of the girl
    • DNot change
    Answer: (A) Be shorter
    Explanation

    Option a is the correct the girl stands up while swinging, the period of will be shorter. The period of a swing is the time for one complete oscillation, which includes one extreme position (e.g., from the highest point side to the highest point on the other side and back). up, the girl shifts her center of mass higher. shortens the length of the pendulum (in this swing chain), which reduces the time it takes for oscillation. Since the period is determined by of the pendulum, increasing the height of the mass effectively shortens the pendulum, resulting in period

28. #28UPSC CSE Prelims 1997
    If the number representing volume and surface area of a cube are equal, then the length of the edge of the cube in terms of the unit of measurement will be
    • A3
    • B4
    • C5
    • D6
    Answer: (D) 6
    Explanation

    Option d is the correct cube is a cuboid that has all sides equal. Surface area of of side 'a' S volume of a cube of side 'a' V that the surface area and volume of a cube equal. S a; So, the side of the cube is 6 units

29. #29UPSC CSE Prelims 1996
    Fat present below the skin surface in our body, acts as a barrier against
    • ALoss of heat from the body
    • BLoss of essential body fluids
    • CLoss of salts from the body
    • DEntry of harmful microorganisms from the environment
    Answer: (A) Loss of heat from the body
    Explanation

    Option a is the correct present below the skin surface in our body, acts barrier against loss of heat from the body. Fat the skin surface in our body is in the form of It is a type of connective tissue that stores fat. It below the skin and between internal organs. The this tissue are filled with fat globules. The storage of as an insulator of body and prevents loss of heat body. This helps in keeping us warm

30. #30UPSC CSE Prelims 1995
    The douds float in the atmosphere because of their low
    • ATemperature
    • BVelocity
    • CPressure
    • DDensity
    Answer: (D) Density
    Explanation

    Option d is the correct answer float in the atmosphere because of their Clouds are formed when warm, moist air rises As the air cools, the water vapor within it tiny water droplets or ice crystals, creating visible These water droplets or ice crystals are dense than the surrounding air, allowing them to and giving clouds their characteristic floating in the atmosphere

31. #31UPSC CSE Prelims 1995
    The difference between nuclear reactor and atom bomb is that
    • AThere is no chain reaction in nuclear reactor whereas this happens in atom bomb
    • BThe chain reaction in nuclear reactor is controlled
    • CThe chain reaction in nuclear reactor is not controlled
    • DAtom bomb is based on nuclear fusion whereas in nuclear reactor, nuclear fission occurs
    Answer: (B) The chain reaction in nuclear reactor is controlled
    Explanation

    Option b is the correct main difference between a nuclear reactor and bomb is that the chain reaction in a nuclear controlled, while the chain reaction in an atom uncontrolled. In a nuclear reactor, the chain reaction by using control rods. Control rods are made (Boron, Cadmium, Hafnium, Indium, and absorb neutrons. When the control rods are the reactor, they absorb some of the neutrons, down the chain reaction. When the control rods from the reactor, they absorb fewer speeds up the chain reaction. In an atom bomb, reaction is not controlled. This is why atom so powerful. When the chain reaction in an atom initiated, it cannot be stopped until all of the has been consumed

32. #32UPSC CSE Prelims 1995
    An air bubble in water will act like a
    • AConvex mirror
    • BConvex lens
    • CConcave mirror
    • DConcave lens
    Answer: (D) Concave lens
    Explanation

    Option d is the correct air bubble in water acts like a concave lens because of in density between air and water. The less dense ( inside the bubble causes light rays to diverge, similar a concave lens works. This divergence results in diminished images, making objects appear smaller away when viewed through the air bubble in water

33. #33UPSC CSE Prelims 1995
    Given below are two statements, one labeled as Assertion and other labeled as Reason Assertion (A): A diamond sparkles more than a glass imitation cut to the same shape. Reason The refractive index of diamond is less than that of glass. In the context of the above two statements, which one of the following is correct?
    • ABoth A and Rare true, and R is the correct explanation of A
    • BBoth A and R are true, but R is not a correct explanation of A
    • CA is true, but R is false
    • DA is false, but R is
    Answer: (C) A is true, but R is false
    Explanation

    Option c is the correct (A) is true: A diamond sparkles more than a cut to the same shape due to its superior Diamonds have a high refractive index, light to slow down and bend as it enters the to multiple internal reflections. This and scatters light, creating the dazzling sparkle "fire:' Glass, with a lower refractive index, lacks the of (R) is false: The refractive index of diamond is refractive index of glass in

34. #34UPSC CSE Prelims 1994
    The heart of human embryo starts beating?
    • AIn the first week of development
    • BIn the third week of its development
    • CIn the fourth week of its development
    • DIn the sixth week of its development
    Answer: (B) In the third week of its development
    Explanation

    Option b is the correct heart of a human embryo starts beating in the of its development. The heart is the first in vertebrate embryos. It begins as two that fuse to form the tubular heart, also called heart tube. The tubular heart then the truncus arteriosus, bulbus cordis, primitive atrium, and the sinus venosus. The elongates and loops, forming an shape. Septa the atria and ventricles to separate the left and of the cardiac tissue starts to contract at around 5-6 weeks registering as a heartbeat on the ultrasound. 10, the fetal heart has developed fully

35. #35UPSC CSE Prelims 1994
    Rennin and lactase, the enzymes required to digest milk, disappear in the human body by the age of
    • ATwo
    • BThree
    • CFive
    • DEight
    Answer: (D) Eight
    Explanation

    Option d is the correct and lactase, the enzymes required to digest in the human body by the age of eight. an enzyme that curdles milk, breaking it down proteins that are easier to digest. Lactase is that breaks down lactose, the sugar in milk, and galactose, which can then be absorbed into produce high levels of both rennin and lactase to digest breast milk. However, as infants get older to eat other foods, their production of these By the age of eight, most people have very low rennin and lactase, and they may experience milk and other dairy is why some people experience lactose is a condition in which the body does not lactase to break down lactose. Symptoms intolerance can include diarrhea, bloating, gas, cramps

36. #36UPSC CSE Prelims 1994
    Water is a good solvent of ionic salts because
    • AIt has a high boiling point
    • BIt has a high dipole moment
    • CIt has a high specific heat
    • DIt has no colour
    Answer: (B) It has a high dipole moment
    Explanation

    Option b is the correct is a good solvent for ionic salts primarily due high dipole moment. A dipole moment is a measure of the separation of positive and negative charges molecule. In the case of water it has a structure with oxygen being more hydrogen, leading to partial negative and on the oxygen and hydrogen atoms, polarity allows water to interact with and in ionic salts. The positive end of water negatively charged ions, while the negative positively charged ions, effectively separating the salt. This unique property of water an essential solvent for various chemical reactions processes. What Happens When Ionic Compounds Dissolve in Water of,llivdy,mion cntlun The force of attraction between ions and the polar water molecule is called the attraction. Partial negative charge Electrons are o- pulled toward Partial positive charge

37. #37UPSC CSE Prelims 1994
    The half-life of a radioactive element is 5 years then the fraction of the radioactive substance that remains after 20 years is
    • A1/2
    • B1/4
    • C1/8
    • D1/16
    Answer: (D) 1/16
    Explanation

    Option d is the correct T 21 5 years, elapsed t 20 the formula of Decay Constant, Inl 2 is decay in values, using here isotope remaining after decaying, amount of isotop decay 0.1386, t elapsed time. Putting values, NO.e NO.e NO 0.0625 Therefore, the fraction of radioactive substances that remains after 20 years is 1/16

38. #38UPPCS 2021
    With reference to radioactivity, which of the following statements is/are correct? 1. Radioactivity is a nuclear property. 2. Hydrogen bomb is prepared on the principle of nuclear fission.Select the correct answer using the codes given below
    • A1 only
    • B2 only
    • CBoth 1 and 2
    • DNeither 1 nor 2
    Answer: (A) 1 only
    Explanation

    Option a is the correct 1 is correct- Radioactivity is a nuclear means that it is caused by changes in the nucleus atom. Radioactivity can occur naturally, or it can 2 is incorrect- Hydrogen bombs are prepared principle of nuclear fusion, not nuclear fission. is the process of combining two or more to form a heavier nucleus. Nuclear fission is of splitting a heavy nucleus into two lighter nuclei. Important Tips Natural radioactivity: Potassium-40 is a naturally radioactive isotope of potassium that decays to argon-40 by emitting a beta particle. Uranium-238 is a naturally radioactive isotope of uranium that decays to lead-206 through a series of alpha and beta decays l Induced radioactivity: Iodine-131 is an artificially radioactive isotope of iodine that can be produced by bombarding uranium-238 with neutrons. Iodine-131 is used to treat thyroid cancer. is an artificially radioactive is

39. #39Previous year
    The stench due to leakage from LPG cylinder is because of: [. (P.re) 2017)
    • AMethane
    • BPropane
    • CButane
    • DEthylmercaptan
    Answer: (D) Ethylmercaptan
    Explanation

    Option dis the correct gas is basically propane and butane. It is odourless in state. The smell that you notice when there is a actually the stench of an entirely different agent, mercaptan. This substance is added to the gas when the main storage mercaptan, also known as ethanethiol, is a contains sulfur and has a very strong and It has the formula

40. #40UPPCS 2013
    Consider the following statement and condusions which can be drawn from it. Choose the correct conclusion. Statement: In starting a loaded cart, one has to push harder than to keep it moving. Condusion
    • AThe weight of a moving object is less
    • BThe wheels tend to slip initially
    • CTh ere is less friction once the cart starts moving
    • DPractice makes perfect
    Answer: (C) Th ere is less friction once the cart starts moving
    Explanation

    Option c is the correct starting a loaded cart, one has to push harder than it moving because of less friction once the cart Friction depends on the nature of the surfaces and the force acting on them. When the cart is there is more interlocking of irregularities between and the ground, which creates more resistance This is called static friction. When the cart the interlocking of irregularities decreases, and becomes less. This is called kinetic friction. is usually less than static friction for the Therefore, one has to push harder to friction than kinetic friction

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