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Chemistry — UPSC Prelims Science & Environment previous year questions

79 solved previous year questions on Chemistry, papers from 1993 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 2021
   Why is there a concern about copper smelting plants? 1. They may release lethal quantities of carbon monoxide into the environment. 2. The copper slag can cause the leaching of some heavy metals into environment. 3. They may release sulphur dioxide as a pollutant.Select the correct answer using the code given below
   • A1 and 2 only
   • B2 and 3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (B) 2 and 3 only
   Explanation

   Option b is the correct 1 is incorrect: Copper smelting does not quantities of carbon monoxide into the monoxide is a byproduct of the reducing the copper ore itself. The amount of carbon depends on the type and quality of the used. Modern copper smelters use coke or coal reducing agent, which have lower carbon than charcoal. Moreover, copper smelters control systems that capture and treat the before releasing it into the 2 is correct: The copper slag is the that is separated from the metal during contains various heavy metals, such as arsenic, and mercury, depending on the composition of the heavy metals can leach into the groundwater or contaminate them. Exposure to these heavy metals serious health problems, such as cancer, kidney damage, and birth 3 is correct: Copper smelting releases a gas that causes acid rain and Most copper ores are sulphur-based, contain sulphur compounds that

2. #2UPSC CSE Prelims 2018
   What is the reason for Non-Metals to be a bad conductor of electricity?
   • AHigh melting point at normal temperature
   • BExcessive free protons around nucleus
   • CAbsence of readily available free electrons
   • DLow resistance to external factors
   Answer: (C) Absence of readily available free electrons
   Explanation

   Option c is the correct takes place due to the movement of Most of the metals are considered as of electricity. This is because when metal with each other, the outermost electrons with their parent atoms. The remaining atomic centers form an ordered structure outer electrons move freely around the whole the other hand, in case of non-metals the are held tightly by the nucleus. So, they easily which means, they do not have free electrons. Hence, the non-metals are not of electricity. However, non-metals can also become good conductors if external energy is applied to them, which conduction electrons Non-metals are considered as insulators have extremely high resistance to the flow of them. The atoms hold onto their electrons so they cannot conduct electricity

3. #3UPSC CSE Prelims 2017
   Consider the following pairs: 25. Commonly Unwanted or used/ consumed controversial materials to produce found in them 1. Lipstick Lead 2. Soft Drinks Brominated vegetable oils 3. Chinese fast Monosodium food glutamateWhich of the pairs given above is/are correctly matched?
   • A1 only
   • B2 and 3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (D) 1, 2 and 3
   Explanation

   Option d is the correct 1 is correctly matched. Lead is a common in cosmetic lip products, such as lipsticks, and such as eye shadows, blushes, compact and body 2 is correctly matched. Brominated vegetable oil is additive sometimes used to keep citrus flavouring out in some sodas and soft drinks. It's banned as additive in Europe and 3 is correctly matched. MSG, is a glutamate, of glutamic acid, a "non-essential" amino acid. It is - transporting messages from one to another. Because it is said to enhance flavours, believe it "excites nerve endings" and properties", that is the ability to It is commonly used in Chinese fast food

4. #4Previous year
   Aspartame is an artificial sweetener sold in the market. It consists of amino adds and provides calories like other amino adds. Yet, it is used as a low-calorie sweetening agent in food items. What is the basis of this use? [UPSC CSE Pre
   • AAspartame is as sweet as table sugar, but unlike table sugar, it is not readily oxidized in the human body due to lack of requisite enzymes
   • BWhen aspartame is used in food processing, the sweet taste remains, but it becomes resistant to oxidation
   • CAspartame is as sweet as sugar but after ingestion into the body, it is converted into metabolites that yield no cal or ies
   • DAspartame is several times sweeter than table sugar, hence food items made with small quantities of aspartame yield fewer cal or ies on oxidation
   Answer: (D) Aspartame is several times sweeter than table sugar, hence food items made with small quantities of aspartame yield fewer cal or ies on oxidation
   Explanation

   Option dis the correct is several times sweeter than table sugar, items made with small quantities of aspartame calories on oxidation. Aspartame is an that is about 200 times sweeter than sugar. that you need much less aspartame to achieve sweetness as sugar. This is why food items made yield fewer calories on oxidation. When ingested, it is broken down into its constituent amino methanol. The body metabolizes these components same way as aspartic acid, L-phenylalanine, and other foods. These components yield no calories nothing to the diet

5. #5Previous year
   A mixture of which one of the following pairs of gases is the cause of occurrence of most of the explosions in mines? [UPSC CSE Pre 2008)
   • AHydrogen and Oxygen
   • BOxygen and Acetylene
   • CMethane and Air
   • DCarbon dioxide and Methane
   Answer: (C) Methane and Air
   Explanation

   Option c is the correct mixture of methane and air is the cause of most of the explosions in mines. Methane, a gas, is frequently encountered in coal mines its release during mining operations, particularly in coal rich seams. When methane combines with the within a specific concentration range (between 5-15 a potentially explosive mixture

6. #6Previous year
   Which one of the following is also called 'Stranger Gas'? [UPSC CSE Pre 2008)
   • AArgon
   • BNeon
   • CXenon
   • DNitrous Oxide
   Answer: (C) Xenon
   Explanation

   Option c is the correct is also referred to as "Stranger Gas:' The originates from the Greek word "Xenos;' "strange or unusual." It is known as "Stranger it exhibits unusual behavior among noble forming compounds with other elements, unlike gas counterparts. This name was coined by American Important Tips Noble gases and their discoverers: Noble Gas First discovered Dfsco- Helium August 18, 1868 Pierre-Jules-Cesar Janssen and Joseph Neon 1898 William Ramsay and Morris W. Travers Argon 1894 William Ramsay and Lord Rayleigh Krypton May 30, 1898 William Ramsay and Morris W. Travers Xenon July 12, 1898 William Ramsay Radon 1900 Friedrich Ernst Dorn Ununoctium 2002 Scientists in the Joint Institute for Laboratory

7. #7UPSC CSE Prelims 2008
   What are Rubies and Sapphires chemically known as?
   • ASilicon Dioxide
   • BAluminium Oxide
   • CLead Tetroxide
   • DBoron Nitride
   Answer: (B) Aluminium Oxide
   Explanation

   Option b is the correct and sapphires are both gems of the mineral is an aluminum oxide with a chemical and a hexagonal crystal structure. The of rubies and sapphires are caused by trace impurities, such as chromium, iron, or titanium, in Corundum is a rock-forming mineral that is igneous, metamorphic, and sedimentary rocks

8. #8UPSC CSE Prelims 2008
   Which one of the following pairs of metals constitutes the lightest metal and the heaviest metal, respectively?
   • ALithium and Mercury
   • BLithium and Osmium
   • CAluminium and Osmium
   • DAluminium and Mercury
   Answer: (B) Lithium and Osmium
   Explanation

   Option b is the correct the lightest metal m the world with a density g/cm 11 3 and osmium is the heaviest metal on a density of 22.5 g/cm 11 3. The other metals in have higher densities than lithium or lower osmium. For example, aluminum has a density of 11 3 and mercury has a density of 13.546 g/cm 11 3. Important Tips Uses of Lithium: Lithium is an effective mood stabilizer that is often used as a long-term treatment for bipolar disorder. Lithium is also used in various industrial applications, such as heat-resistant glass and ceramics, lithium grease lubricants, flux additives for iron, steel and aluminium production, lithium metal batteries, and lithium-ion batteries. Lithium alloys with other metals, such as magnesium and aluminium, increase their strength and reduce their weight. These alloys are used in making armor platings, airplane parts, bicycle frames, etc. Uses of Osmium: O

9. #9UPSC CSE Prelims 2003
   Consider the following statements:Sodium silicate and sodium sulphate are mixed as detergents in washing powders so that- 1. To maintain the dryness of the powder. 2. To maintain the basicity of powder.Which of the following statements is correct?
   • A1 only
   • B2 only
   • CBoth 1 and 2
   • DNeither 1 nor 2
   Answer: (C) Both 1 and 2
   Explanation

   Option c is the correct 1 is correct: Sodium sulphate is mixed powders to maintain the dryness of the sulfate is a desiccant, meaning it has the ability moisture and keep the powder dry. This and ensures the powder remains free-flowing to dispense. The dryness of the powder is essential storage and effective use of the 2 is correct: Sodium silicate is added to to maintain their basicity (alkalinity). It helps the pH of the detergent, making it more removing stains and dirt from clothes. Basic favorable for the cleaning action of detergents, breaking down acidic substances like grease and oils

10. #10UPSC CSE Prelims 2003
    With reference to ionic compounds, consider the following statements: 1. Ionic compounds are insoluble in alcohol. 2. Ionic compounds in the solid state are a good conductor of electricity.Which of these statements is/are correct?
    • 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: Ionic compounds are in alcohol due to differences in polarity. consist of positively and negatively charged together by strong electrostatic forces. Polar solvents can disrupt these forces and dissolve ionic surrounding and separating the ions. However, less polar than water, resulting in weaker the ions. As a result, many ionic compounds do in alcohol, making them relatively insoluble 2 is incorrect: Ionic compounds in the solid generally not good conductors of electricity. In their the ions in an ionic compound are locked in a lattice structure, and there are no mobile (like free electrons) that can carry an However, when ionic compounds are melted in water (in the molten or aqueous state), the mobile and can conduct electricity. So, while can conduct electricity in certain states, they in their solid form

11. #11UPSC CSE Prelims 2003
    With reference to normal human beings, consider the following statements: 1. In response to the presence of HCI, secretin is produced from the duodenum. 2. Enterogastrone is produced in the small intestine in response to the presence of fatty acidsWhich of these statements is/are correct?
    • A1 only
    • B2 only
    • CBoth 1 and 2
    • DNeither 1 nor 2
    Answer: (C) Both 1 and 2
    Explanation

    Option c is the correct 1 is correct: In response to the presence acid in the duodenum, the is produced and released. Secretin is released bloodstream when the pH of the duodenum a certain level. Secretin helps regulate the pH small intestine by stimulating the pancreas to pancreatic juice, which neutralizes chyme coming from the 2 is also correct: Enterogastrone, which like cholecystokinin (CCK) and gastric (GIP), is produced in the small intestine in the presence of fatty acids. Enterogastrone is a inhibits gastric acid secretion and gastric motility. released into the bloodstream when fatty acids enter intestine. Enterogastrone is thought to play a role the stomach from being overloaded with fat. It also helps to slow down the digestion of which gives the body more time to absorb them

12. #12UPSC CSE Prelims 2002
    Consider the following statements: Assertion (A): Human diet should compulsorily contain glycine, serine and tyrosine. Reason Essential amino acids cannot be synthesized in the human body. 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: Glycine, serine and tyrosine are amino acids for humans. They are classified or conditionally essential, meaning they can by the body under normal (R) is true: Essential amino acids are amino cannot be synthesized from scratch by the enough to supply its demand, and must therefore the diet. The nine essential amino acids for histidine, isoleucine, leucine, lysine, threonine, tryptophan and valine m Important Tips Amino acids are the building blocks of protein. They are involved in many important roles in your body, such as: Breaking down food and providing energy. Growing and repairing body tissue, such as muscles, skin, hair and nails. Making hormones and brain chemicals (neurotransmitters) that regulate your mood, sleep, memory and cognition. Maintaining healthy immune function and fighting infections. Supporting the production of collagen and elas

13. #13UPSC CSE Prelims 2001
    Consider the following statements with reference to the periodic table of chemical elements: 1. Ionization potential gradually decreases along a period. 2. In a group of elements, electron affinity decreases as the atomic weight increases. 3. In a given period, electronegativity decreases as the atomic number increases.Which of these is/are correct?
    • A1 only
    • B2 only
    • C1 and 3 only
    • D2 and 3 only
    Answer: (B) 2 only
    Explanation

    Option b is the correct 1 is incorrect because ionization increases along a period, not decreases. This the atomic radius decreases and the nuclear as we move from left to right across a it harder to remove an electron from the 2 is correct because electron affinity the atomic weight increases in a group of is because the atomic radius increases and the charge decreases as we move down a group, less favorable for an atom to gain an 3 is incorrect because electronegativity the atomic number increases in a given period, This is because the atomic radius decreases nuclear charge increases as we move from left to a period, making it easier for an atom to attract with electrons

14. #14UPSC CSE Prelims 2001
    Consider the following statements: Assertion (A): A piece of copper and a piece of glass are heated to the same temperature. When touched, thereafter, the copper piece appears hotter than the glass piece. Reason The density of copper is more than that of glass. Code
    • 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 true
    Answer: (B) Both A and R are true, but R is not a correct explanation of A
    Explanation

    Option b is the correct (A) is correct: When a piece of copper and a glass are heated to the same temperature, the copper hotter than the glass piece when touched is because metals like copper conduct heat much than non-metals like glass. Therefore, they are at the same temperature, the copper transfer more heat to your skin, making it feel (R) is correct, but R is not a correct A: Reason (R) states that the density of copper is that of glass. While this is true (copper is denser it is not directly related to the phenomenon Assertion (A). Density of a material does not thermal conductivity. Density is a measure of mass a material has per unit volume, and it does how fast heat can flow through it

15. #15UPSC CSE Prelims 2000
    Which one of the following materials is very hard and very ductile?
    • ACarborundum
    • BTungsten
    • CCast iron
    • DNichrome
    Answer: (D) Nichrome
    Explanation

    Option d is the correct is a non-magnetic alloy of nickel, chromium, usually used as a resistance wire. A common alloy is and chromium by mass. This alloying properties like hardness and ductility. a tensile test elongation of which indicates its is a very hard material, but it is not ductile. a synthetic compound of silicon and carbon, also silicon carbide. It has a Mohs hardness of 9.5, which than most metals and minerals. However, it is fractures easily under is also a very hard material, but it is not It is a metallic element with the highest and the highest tensile strength of all metals. It has hardness of 3430-4600 and a Brinell hardness However, it has low ductility and room temperature and becomes more ductile at iron is not very hard nor very ductile. It is an iron and carbon, with a carbon content of more It has a Brinell hardness of 200-1180 the type and composition of cast i

16. #16UPSC CSE Prelims 2000
    Canola refers to a special type of oilseed mustard varieties breed for human consumption. The main characteristic of these varieties is that the
    • ASeeds have very high oil content
    • BOil is rich in unsaturated fatty acids
    • COil has long shelf-life
    • DOil has very low erucic acid content
    Answer: (D) Oil has very low erucic acid content
    Explanation

    Option d is the correct is a type of oilseed rape that has been for its low erucic acid content. Erucic acid is fatty acid that can be harmful to in high doses. Canola oil contains less than which is considered to be safe for human oil is also a good source of unsaturated fatty are beneficial for human health. Unsaturated can help to lower cholesterol levels and reduce of heart disease

17. #17UPSC CSE Prelims 1999
    Which one of the following is a useful functional association between fungi and the roots of higher plants?
    • ABiofertilizer
    • BCoralloid root
    • CLichens
    • DMycorrhiza
    Answer: (D) Mycorrhiza
    Explanation

    Option d is the correct useful functional association between fungi roots of higher plants is known as associations are mutualistic fungi colonize the plant's root system. These the root's reach into the soil, increasing the plant's ability to absorb essential nutrients, particularly nitrogen. In return, the plant provides the fungi and other organic compounds produced Mycorrhizal symbiosis is vital for in many plants and contributes to their growth It can be considered a natural form ofbiofertilization

18. #18UPSC CSE Prelims 1999
    Consider the following statements:Glass can be etched or scratched by- 1. Diamond 2. Hydrofluoric Acid 3. Aquaregia 4. Cone. Sulphuric AcidWhich of these statements are correct?
    • A1 and 4 only
    • B2 and 3 only
    • C1 and 2 only
    • D2 and 4 only
    Answer: (C) 1 and 2 only
    Explanation

    Option c is the correct can scratch glass: Diamond is one of the known, and it can easily scratch glass Acid can etch or dissolve glass: It is one few acids that can react with silicon dioxide, which primary component of glass. Hydrofluoric acid is glass etching and can create intricate patterns or glass regia cannot scratch glass: Aqua regia is a nitric acid and hydrochloric acid. While it is a for dissolving noble metals like gold it doesn't readily react with acid cannot scratch glass: Sulfuric acid, not able to dissolve glass, which is why it can be in a glass container. This is because sulfuric acid not corrosive enough to eat through the silicon dioxide bonds that are the found in glass

19. #19UPSC CSE Prelims 1999
    Consider the following statements regarding a motor car battery: 1. The voltage is usually 12 V. 2. Electrolyte used is hydrochloric acid. 3. Electrodes are lead and copper. 4. Capacity is expressed in ampere-hour.Which of the above statements are correct?
    • A1 and 2
    • B2 and 3
    • C3 and 4
    • D1 and 4
    Answer: (D) 1 and 4
    Explanation

    Option d is the correct l is correct- The voltage of a car battery is 2 is incorrect- The electrolyte used in a is sulfuric acid, not hydrochloric 3 is incorrect- The electrodes in a car battery of lead and antimony, not 4 is correct- The capacity of a car battery in ampere-hours

20. #20UPSC CSE Prelims 1998
    Consumption of fish is considered to be healthy when compared to the flesh of other animals because fish contains
    • APolyunsaturated fatty acids
    • BSaturated fatty acids
    • CEssential vitamins
    • DMore carbohydrates and proteins
    Answer: (A) Polyunsaturated fatty acids
    Explanation

    Option a is the correct contains more polyunsaturated fatty acids than which act as natural antioxidants and lower of heart disease. Polyunsaturated fatty acids have one double bond in their structure, which makes flexible and fluid. Some examples of acids are omega-3 and omega-6, which are essential health. fatty acids have only single bonds in their makes them more rigid and solid. They are found fats, such as butter, lard, and cheese, and can level of bad cholesterol in the blood. Excess intake fat can increase the risk of coronary artery disease

21. #21UPSC CSE Prelims 1998
    Consider the following statements about acetylene: 1. It is used in the welding industry. 2. It is a raw material for preparing plastics. 3. It is easily obtained by mixing silicon carbide and water. Of these statements
    • A1 and 2 are correct
    • B1 and 3 are correct
    • C2 and 3 are correct
    • D1, 2 and 3 are correct
    Answer: (A) 1 and 2 are correct
    Explanation

    Option a is the correct is a hydrocarbon compound. It is the and has a triple bond between the two carbon is a colorless gas with a distinctive odor and is widely a fuel and a chemical building 1 is correct: It is used in the welding has a very high flame temperature of about when burned with oxygen. It is used for and cutting of 2 is correct: It is a raw material for Acetylene can be used to synthesize various such as vinyl chloride, acetaldehyde, and acrylonitrile. These compounds are making plastics such as polyvinyl chloride terephthalate (PET), and 3 is incorrect: Acetylene is not produced silicon carbide and water. Silicon carbide water to produce silicon dioxide and methane, The common method of producing acetylene is of calcium carbide, which gives calcium acetylene

22. #22UPSC CSE Prelims 1998
    Consider the following statements: Assertion (A): Sodium metal is stored under kerosene. Reason Metallic sodium melts when exposed to air. 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: (C) (A) is true, but (R) is false
    Explanation

    Option c is the correct (A) is true: Sodium metal is stored under it reacts very rapidly with oxygen and water in forming sodium hydroxide and sodium can corrode the metal and cause fire (R) is false: Metallic sodium does not melt to air, but it does melt at a low temperature

23. #23UPSC CSE Prelims 1998
    Consider the following statements: Assertion (A): Formic Acid is a stronger acid than Acetic acid. Reason Formic Acid is an organic acid. 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: (B) Both (A) and (R) are true, but (R) is not the correct explanation of (A)
    Explanation

    Option b is the correct (A) is true: Formic acid is a stronger acid acid because it can lose proton more easily to The strength of an acid depends on the stability conjugate base. The more stable the conjugate base, the acid. Formic acid has the chemical and its conjugate base is CHO2-. Acetic acid chemical formula and its conjugate base is The conjugate base of formic acid does not have group, so it is more stable and can proton more easily. This strengthens the acidity of (R) is true: Formic acid is the simplest organic the chemical formula HCOOH. It is also known acid or formylic acid. It has a pungent, and a colourless appearance. It is an in chemical synthesis and occurs naturally ants and other insects. (R) is not the correct explanation of (A): Organic acid necessarily mean being a stronger acid. Organic acids that contain carbon atoms in their molecules. There organic acids that

24. #24UPSC CSE Prelims 1997
    Which one of the following is present in the largest amount in terms of percent by mass in the earth's crust?
    • ASilicon
    • BOxygen
    • CCarbon
    • DCalcium
    Answer: (B) Oxygen
    Explanation

    Option b is the correct is the most abundant chemical element in crust, making up of its mass. Silicon is most abundant element, with of the and calcium are much less abundant, with respectively. Therefore, oxygen is present in amount of mass in the Earth's crust

25. #25UPSC CSE Prelims 1997
    The characteristic odour of garlic is due to
    • AA chloro compound
    • BA sulphur compound
    • CA fluorine compound
    • DAcetic acid
    Answer: (B) A sulphur compound
    Explanation

    Option b is the correct answer. The characteristic odour of garlic is due to a called allicin. Allicin is produced when crushed or chewed. It is a volatile compound, it easily evaporates. This is why the smell of garlic strong. Allicin has a number of health benefits. It antiviral, and antifungal properties. It has shown to reduce cholesterol levels and lower

26. #26UPSC CSE Prelims 1997
    Which one of the following is used as an anti-freeze for automobile engines?
    • APropyl alcohol
    • BEthanol
    • CMethanol
    • DEthylene glycol
    Answer: (D) Ethylene glycol
    Explanation

    Option d is the correct glycol is a chemical compound that is mixed to lower the freezing point and raise the boiling the engine coolant. It also helps to prevent corrosion cooling glycol has a unique property that allows it to freezing point of water. When mixed with water in proportions, it creates a solution with a freezing point than pure water. This is crucial in where the temperature can drop below the of water

27. #27UPSC CSE Prelims 1996
    Living organisms require at least 27 elements, of which, 15 are Among these, those required in major quantities, indude
    • APotassium, manganese, molybdenum and calcium
    • BPotassium, molybdenum, copper and calcium
    • CPotassium, sodium, magnesium and calcium
    • DSodium, magnesium, copper and manganese
    Answer: (C) Potassium, sodium, magnesium and calcium
    Explanation

    Option c is the correct organisms need a variety of elements for and metabolism. Among the 27 elements are needed in larger quantities than others. elements include potassium, sodium, calcium. Potassium is essential for nerve and sodium plays a role in maintaining fluid is crucial for various cellular processes, is vital for bone health, muscle function, and elements are fundamental for the proper living organisms

28. #28UPSC CSE Prelims 1994
    Which one of the following is the correct sequential order in which these appeared under simulated primitive earth condition?
    • AMethane, Hydrogen Cyanide, Nitrile, Amino Acid
    • BHydrogen Cyanide, Methane, Nitrile, Amino Acid
    • CAmino Acid, Nitrile, Hydrogen Cyanide, Methane
    • DNitrile, Amino Acid, Methane, Hydrogen Cyanide
    Answer: (A) Methane, Hydrogen Cyanide, Nitrile, Amino Acid
    Explanation

    Option a is the correct correct sequential order in which these simulated primitive earth condition is Cyanide, Nitrile, Amino Acid. This is based famous Miller-Urey experiment, which simulated of the early Earth's atmosphere and oceans to organic molecules could be formed from The experiment used water methane (NIB), hydrogen (H2), and an electric arc lightning. The results showed that amino acids organic molecules were produced from the methane and hydrogen cyanide, which were from the breakdown of ammonia by the Nitriles are a type of organic compound that carbon-nitrogen triple bond, and they can be derived cyanide as well. Therefore, the sequential appearance of these molecules under the Earth condition is methane, hydrogen and amino acid

29. #29UPSC CSE Prelims 1993
    The Government of India has totally banned the export of burnt coal (Jhama) because it contains recoverable amount of a metal/ element which is used in transistors. Which one of the following is that element?
    • APhosphorus
    • BGermanium
    • CSilicon
    • DTungsten
    Answer: (B) Germanium
    Explanation

    Option b is the correct coal (Jhama) contains recoverable amounts which is a metal/element used in is a semiconductor material, which it has electrical conductivity between that of and an insulator. This makes it ideal for electronic devices, such as transistors. Transistors to amplify and switch electrical signals, and they components of many electronic devices, including computers, smartphones, and TVs. Germanium is also other electronic devices, such as infrared detectors cells. The Government of India has banned the burnt coal in order to conserve the country's Important Tips Some additional details about germanium: Germanium is a silvery-white metal that is found in the Earth's crust. It is a relatively rare element, but it is still relatively abundant compared to other semiconductors, such as gallium arsenide. Germanium is also relatively easy to process, making it a cost-effective

30. #30UPSC CSE Prelims 1993
    Consider the figures of a metal ball and a metal ring given below: Ball Annulus The metal ball can just pass through the hole of a metal ring formed out of a strip. When the ball is heated it gets stuck. But when the metal is heated
    • AThe ball can still pass through the ring as diameter expands on heating
    • BThe ball gets stuck because the diameter of the hole decreases on expansion
    • CThe ball will still pass through because the hole diameter does not change
    • DThe ball will pass through because there is no change in the ring
    Answer: (A) The ball can still pass through the ring as diameter expands on heating
    Explanation

    Option a is the correct the experiment, the ball and the ring are made of metal, so they have the same rate of thermal they are at the same temperature, the ball can just the ring, because the diameter of the ball is than the diameter of the ring. However, when is heated, it expands more than the ring, because it volume to expand. This makes the diameter of the than the diameter of the ring, and the ball gets both the ball and the ring are heated, they both the same amount, because they have the same rate expansion. This means that the difference diameters remains constant, and the ball can still the ring. The ball does not get stuck because ball and the ring have increased in size proportionally

31. #31UPPCS 2019
    Tulsi plant has medicinal values due to the presence of the following
    • AInorganic Acid
    • BOrganic Acid
    • CPhenols and Flavonoids
    • DNone of the above
    Answer: (C) Phenols and Flavonoids
    Explanation

    Option c is the correct and flavonoids are natural compounds that in many plants, including tulsi. These a wide range of medicinal properties, Phenols and flavonoids help to protect from damage caused by free radicals. Free unstable molecules that can damage cells and lead such as cancer and heart Phenols and flavonoids have anti inflammatory properties. Inflammation is a root cause diseases, such as arthritis, asthma, and and antiviral: Phenols and flavonoids and antiviral properties. They can help off infections and boost the immune plants are also a good source of vitamins and as vitamin calcium, and iron

32. #32UPPCS 2016
    Digestion of Lipids takes place in the presence of some of the following: 1. Bile acids 2. Lipase 3. Pepsin Of these
    • AOnly 1 is correct
    • BOnly 1 and 3 are correct
    • COnly 1 and 2 are correct
    • D1, 2 and 3 are correct
    Answer: (C) Only 1 and 2 are correct
    Explanation

    droplets, increasing the surface area available for Option c is the correct answer, enzymes to act upon. This process aids in the digestion of lipids (fats) takes place in the presence and absorption of bile acids and lipase. Pepsin is a protease that digests Lipase: Lipase is an enzyme responsible for down lipids (fats) into smaller components, such as fatty Bile acids: Bile acids, produced by the liver and stored acids and glycerol. Lipase is produced by the pancreas in the gallbladder, play a crucial role in lipid digestion. and released into the small intestine. It catalyzes the They are released into the small intestine when needed. hydrolysis of triglycerides, which are dietary fats, into Bile acids help emulsify large lipid molecules into smaller absorbable forms that can be taken up by the body. Pepsin: Pepsin is an enzyme secreted by the stomach to At normal temperatures, they l

33. #33UPPCS 2015
    The resistance of a semiconductor on heating
    • ARemains constant
    • BDecreases
    • CIncreases
    • DNone of the above
    Answer: (B) Decreases
    Explanation

    that is made from petroleum and coal. Nylon is an Option b is the correct answer. of an addition polymer that is formed by the reaction of diamines and dicarboxylic resistance of a semiconductor decreases on heating. because heating increases the number of charge carriers A natural polymer is a polymer that is obtained from the semiconductor. The charge carriers are electrons and organisms, such as plants and animals. Natural Electrons are negatively charged particles that can are formed by the process of addition polymerization freely through the semiconductor. Holes are positively condensation polymerization. Some examples of spaces left behind when electrons move. When a polymers are cellulose, chitin, carbohydrates, proteins, is heated, the atoms in the semiconductor RNA, and natural more. This vibration can cause electrons to break free 285. Solution: their bonds and become mobile c

34. #34UPPCS 2012
    Which one of the following adds is used in the manufacturing of baking powder?
    • AOxalic Acid
    • BLactic Acid
    • CTartaric Acid
    • DBenzoic Acid
    Answer: (C) Tartaric Acid
    Explanation

    Option c is the correct acid is used in the manufacturing of baking acid is one of the acids commonly used in When it comes into contact with a base bicarbonate, or baking soda) in the presence (like in a dough or batter), it undergoes a that releases carbon dioxide gas. This gas which leaven the dough or batter, making it rise light and airy

35. #35UPPCS 2010
    Which one of the following is not
    • ABordeaux mixture is a mixture of copper (II) sulphate and calcium hydroxide in water and is used as a fungicide
    • BBoric acid is used in pharmaceutical industry and also as a food preservative
    • CDry ice is solid carbon dioxide
    • DNitric oxide is laughing gas
    Answer: (D) Nitric oxide is laughing gas
    Explanation

    Option d is the correct oxide (NO) is not laughing gas. Laughing gas oxide, which has the chemical formula oxide is a colorless and odorless gas that is in the body. It has a number of functions, including regulating blood vasodilating blood vessels. Nitric oxide is also used number of medical applications, such as treating and pulmonary gas refers to nitrous oxide which is used anesthetic and has mild euphoric effects when to its association with laughter or giggling, name "laughing gas"

36. #36UPPCS 1996
    Which one of the following forms an irreversible complex with a hemoglobin of the blood?
    • ACarbon Dioxide
    • BPure Nitrogen gas
    • CCarbon Monoxide
    • DA mixture of Carbon Dioxide and Helium
    Answer: (C) Carbon Monoxide
    Explanation

    Option c is the correct monoxide is a colorless, odorless, tasteless gas produced by the incomplete combustion of fossil is a highly toxic gas that can be fatal if inhaled in Carbon monoxide forms an with hemoglobin, the oxygen-carrying protein blood cells. This complex is called cannot carry oxygen, which can hypoxia, a condition in which the body's tissues do enough oxygen

37. #37UPSC CDS 2020
    Scattering of a-particles by a thin gold foil suggests the presence of
    • Aelectron in an atom
    • Bproton in an atom
    • Cpositively charged nucleus at the centre of an atom
    • Disotopes of gold
    Answer: (C) positively charged nucleus at the centre of an atom
    Explanation

    Option c is the correct scattering of alpha particles by a thin gold foil, as the famous experiment conducted by Ernest to the conclusion that most of the mass and of an atom is concentrated in a small, dense the nucleus. This discovery suggested the presence positively charged nucleus at the center of an atom, surrounded by negatively charged electrons

38. #38UPSC CDS 2023
    A Sprinter feels crapms and pain in the thigh muscles after a run. This is due to accumulation of
    • Alactic acid
    • BCO 2
    • Cpyruvic acid
    • Dethanol
    Answer: (A) lactic acid
    Explanation

    Option a is the correct intense exercise, when oxygen supply to the limited, the muscles switch to anaerobic metabolism. process, pyruvate is converted into lactic acid fermentation pathway called lactate accumulation of lactic acid in the muscles can lead sensation of cramps and pain. It is commonly muscle fatigue and is a normal response to The cramps and pain usually subside as the is metabolized and cleared from the muscles

39. #39UPSC CDS 2022
    Methanoic acid is normally found in
    • Amuscles
    • Burine
    • Cant stings
    • Dhuman brain
    Answer: (C) ant stings
    Explanation

    Option c is the correct acid, also known as formic acid, is a liquid that is found in the stings of is a weak acid, but it can cause a burning sensation at the site of the sting

40. #40UPSC CDS 2022
    Which of the following mineral adds is found in the human stomach?
    • AHydrochl or ic acid
    • BLactic acid
    • CUric acid
    • DMethanoic acid
    Answer: (A) Hydrochl or ic acid
    Explanation

    Option a is the col'l'ect answer Hydrochloric acid is a mineral acid that is found in stomach. It helps to break down food and Lactic acid, uric acid, and methanoic acid are acids

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