Chemistry MCQs

Question #21

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The SI unit of calorific value is:

A. Joule per kilogram

B. Pascal

C. Watt

D. Kilocalorie per gram

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Correct Answer: Option A

Explanation:
Calorific value is the amount of heat energy produced by complete combustion of unit mass of a fuel. SI unit is J/kg, often expressed as kJ/kg or MJ/kg. Previously, kcal/kg or cal/g was used. 1 cal = 4.184 J. Higher calorific value indicates better fuel. Example: hydrogen has very high calorific value ~150 MJ/kg. Exam note: Calorific value is measured by bomb calorimeter.

This question belongs to: Science chemistry

Question #22

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Which of the following is a renewable fuel source?

A. Petroleum

B. Biofuel

C. Natural gas

D. Coal

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Correct Answer: Option B

Explanation:
Biofuels like ethanol (from sugarcane), biodiesel (from plant oils), and biogas (from organic waste) are renewable as they can be replenished within a human lifespan. Coal, petroleum, and natural gas are fossil fuels, formed over millions of years, and are non-renewable. Using renewable fuels helps reduce greenhouse gas emissions. Another renewable fuel is hydrogen produced from water electrolysis using solar power.

This question belongs to: Science chemistry

Question #23

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During electrolysis, reduction takes place at the:

A. Electrolyte

B. Cathode

C. Salt bridge

D. Anode

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Correct Answer: Option B

Explanation:
In an electrochemical cell, reduction (gain of electrons) always occurs at the cathode, regardless of whether the cell is electrolytic or galvanic. At the anode, oxidation (loss of electrons) occurs. Memory aid: 'RED CAT' (REDuction at CAThode), 'AN OX' (OXidation at ANode). In electrolysis, the cathode is connected to the negative terminal of the battery, attracting cations which get reduced.

This question belongs to: Science chemistry

Question #24

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According to Faraday's first law of electrolysis, the mass of substance deposited is directly proportional to:

A. Quantity of electricity passed

B. Time of electrolysis

C. Electrode area

D. Current passed

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Correct Answer: Option A

Explanation:
Faraday's first law: m ∝ Q, where m = mass deposited, Q = charge passed (current × time). So mass deposited is directly proportional to the quantity of electricity (coulombs). While m ∝ I and m ∝ t individually are true for constant parameters, the exact law states m = ZIt = ZQ, where Z is electrochemical equivalent. The law directly links mass to Q. Faraday's second law deals with equivalent masses.

This question belongs to: Science chemistry

Question #25

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Boyle's law relates which two variables at constant temperature?

A. Pressure and temperature

B. Number of moles and volume

C. Volume and temperature

D. Pressure and volume

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Correct Answer: Option D

Explanation:
Boyle's law states that at constant temperature, the volume of a given mass of gas is inversely proportional to pressure: PV = constant. So P ∝ 1/V. Charles' law relates V and T at constant P. Gay-Lussac's law relates P and T at constant V. Boyle's law is used in syringes and scuba diving. Graph of P vs V is a hyperbola; P vs 1/V is a straight line.

This question belongs to: Science chemistry

Question #26

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Which gas will diffuse fastest under identical conditions?

A. N₂

B. O₂

C. CO₂

D. NH₃

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Correct Answer: Option D

Explanation:
Rate of diffusion is inversely proportional to the square root of molar mass (Graham's law). Lighter gases diffuse faster. Molar masses: NH₃ = 17, N₂ = 28, O₂ = 32, CO₂ = 44 g/mol. Therefore NH₃ has the lowest molar mass and diffuses fastest. This law also explains why the smell of perfume spreads quickly. NH₃ is lighter than air and would rise.

This question belongs to: Science chemistry

Question #27

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Which catalyst is used in the hydrogenation of vegetable oils?

A. Pt

B. Fe

C. V₂O₅

D. Ni

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Correct Answer: Option D

Explanation:
Nickel (finely divided) is used as a catalyst in the hydrogenation of unsaturated vegetable oils to saturated fats (vanaspati ghee). The reaction adds H₂ across double bonds. Platinum and palladium are also hydrogenation catalysts but nickel is cheaper and industrially preferred. Fe is used in Haber process for ammonia synthesis, V₂O₅ in contact process for H₂SO₄. Catalysts provide an alternative pathway with lower activation energy.

This question belongs to: Science chemistry

Question #28

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An enzyme is a:

A. Proteinaceous biocatalyst

B. Inorganic catalyst

C. Negative catalyst

D. Lipid catalyst

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Correct Answer: Option A

Explanation:
Enzymes are proteinaceous substances that act as biological catalysts, speeding up biochemical reactions in living organisms without being consumed. They are highly specific and work under mild conditions (pH, temperature). Examples: amylase breaks down starch, pepsin digests proteins. Inorganic catalysts are like Pt, Ni. Lipids are fats, not catalysts. Negative catalysts (inhibitors) slow reactions. Enzymes may be deactivated by high temperature or extreme pH.

This question belongs to: Science chemistry

Question #29

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The process of extracting a metal by heating its oxide ore with a reducing agent is called:

A. Leaching

B. Calcination

C. Roasting

D. Smelting

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Correct Answer: Option D

Explanation:
Smelting involves heating a metal oxide ore (roasted or calcined) with a reducing agent like coke (carbon) or CO to obtain the metal in the molten state. Example: Fe₂O₃ + 3CO → 2Fe + 3CO₂ in blast furnace. Calcination: heating carbonate/ hydroxide ore in absence of air. Roasting: heating sulfide ore in excess air. Leaching: chemical dissolution of ore. Smelting is a key pyrometallurgical step.

This question belongs to: Science chemistry

Question #30

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Which ore is concentrated by froth flotation process?

A. Magnetite

B. Bauxite

C. Carnallite

D. Galena

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Correct Answer: Option D

Explanation:
Froth flotation is used to concentrate sulfide ores. Galena (PbS) is a sulfide ore; it is wetted by oil (pine oil) and comes to the surface with froth, while gangue particles wetted by water settle down. Bauxite (Al₂O₃·2H₂O) is an oxide ore concentrated by leaching (Bayer's process). Magnetite (Fe₃O₄) is magnetic ore separated by magnetic separation. Carnallite (KCl·MgCl₂·6H₂O) is a halide ore.

This question belongs to: Science chemistry

Question #31

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Urea is a widely used nitrogenous fertilizer. Its nitrogen content by mass is approximately:

A. 21%

B. 82%

C. 35%

D. 46%

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Correct Answer: Option D

Explanation:
Urea, CO(NH₂)₂, molar mass = 60 g/mol. Mass of N = 2×14 = 28 g. Percentage N = (28/60) × 100 ≈ 46.67%, commonly rounded to 46%. It has the highest nitrogen content among solid fertilizers, making it economical. DAP (diammonium phosphate) has 18% N and 46% P₂O₅. Ammonium nitrate has 33% N. Urea is converted to ammonia and carbon dioxide by soil urease enzyme.

This question belongs to: Science chemistry

Question #32

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NPK fertilizer supplies which primary nutrients?

A. Nitrogen, Potassium, Calcium

B. Nitrogen, Phosphorus, Potassium

C. Sodium, Phosphorus, Potassium

D. Nitrogen, Phosphorus, Calcium

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Correct Answer: Option B

Explanation:
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K), the three primary macronutrients essential for plant growth. N promotes leaf growth, P aids root and flower development, K supports overall health. Fertilizer labels like 10-26-26 indicate the percentages of N, P₂O₅, and K₂O respectively. Calcium, magnesium, and sulfur are secondary nutrients, while Fe, Mn, Zn etc. are micronutrients.

This question belongs to: Science chemistry

Question #33

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Which acid is known as 'Oil of Vitriol'?

A. Nitric acid

B. Sulphuric acid

C. Hydrochloric acid

D. Acetic acid

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Correct Answer: Option B

Explanation:
Sulphuric acid (H₂SO₄) is historically called oil of vitriol because it was prepared by distilling green vitriol (ferrous sulfate heptahydrate). It is a dense, oily liquid. Nitric acid is aqua fortis, hydrochloric acid was called muriatic acid or spirit of salt. Sulphuric acid is the king of chemicals due to its widespread use in industries like fertilizer, petroleum refining, and chemical synthesis.

This question belongs to: Science chemistry

Question #34

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Hydrogen peroxide (H₂O₂) is stored in dark colored bottles because it:

A. Decomposes in presence of light

B. Evaporates quickly

C. Reacts with glass

D. Absorbs moisture

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Correct Answer: Option A

Explanation:
H₂O₂ decomposes when exposed to light (photochemical decomposition): 2H₂O₂ → 2H₂O + O₂. Light provides energy to break the O–O bond. To prevent decomposition, it is stored in amber or opaque bottles, often with stabilizers like urea or phosphoric acid. Also, traces of heavy metal ions catalyze decomposition. H₂O₂ is a strong oxidizing agent and bleaching agent.

This question belongs to: Science chemistry

Question #35

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The functional group present in methanol is:

A. Carboxylic acid

B. Aldehyde

C. Alcohol

D. Ketone

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Correct Answer: Option C

Explanation:
Methanol (CH₃OH) contains the hydroxyl (–OH) functional group characteristic of alcohols. It is the simplest alcohol, also called wood alcohol. Ethanol (C₂H₅OH) is the alcohol in beverages. Aldehydes have –CHO group, ketones have >C=O, carboxylic acids have –COOH. Methanol is toxic; ingestion can cause blindness or death. It is used as a solvent and in formaldehyde production.

This question belongs to: Science chemistry

Question #36

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Soap is formed by the alkaline hydrolysis of fats and oils. This reaction is called:

A. Saponification

B. Esterification

C. Hydrogenation

D. Emulsification

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Correct Answer: Option A

Explanation:
Saponification is the hydrolysis of triglycerides (fats/oils) with NaOH or KOH to produce glycerol and the sodium or potassium salts of long-chain fatty acids, which are soaps. Esterification is the formation of esters from acid and alcohol. Emulsification is the dispersion of one liquid in another. Hydrogenation is addition of H₂. Hard soaps use NaOH, soft soaps use KOH. Soaps clean by micelle formation.

This question belongs to: Science chemistry

Question #37

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Which of the following polymers is used as a non-stick coating in cookware?

A. Nylon

B. Teflon

C. PVC

D. Polystyrene

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Correct Answer: Option B

Explanation:
Teflon is polytetrafluoroethylene (PTFE), a fluorocarbon polymer with extremely low coefficient of friction and high thermal stability, making it ideal for non-stick cookware. PVC (polyvinyl chloride) is used in pipes and cables. Polystyrene is used in packaging and insulation. Nylon is a polyamide used in textiles. Teflon is chemically inert and resistant to acids and bases.

This question belongs to: Science chemistry

Question #38

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Cement is a mixture of calcium silicates and aluminates. The main raw materials for its manufacture are:

A. Chalk and soda ash

B. Limestone and clay

C. Gypsum and sand

D. Marble and quartz

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Correct Answer: Option B

Explanation:
Portland cement is made by heating a mixture of limestone (CaCO₃) and clay (containing SiO₂, Al₂O₃, Fe₂O₃) in a rotary kiln at high temperature, forming clinker, which is then ground with a small amount of gypsum to control setting. Gypsum alone is added as a retarder, not raw material. The major compounds formed are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite.

This question belongs to: Science chemistry

Question #39

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Hard water contains dissolved salts of calcium and magnesium. Which substance causes temporary hardness?

A. Calcium bicarbonate

B. Sodium bicarbonate

C. Calcium sulfate

D. Magnesium chloride

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Correct Answer: Option A

Explanation:
Temporary hardness is due to dissolved bicarbonates of Ca and Mg, which can be removed by boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Permanent hardness is caused by chlorides and sulfates of Ca and Mg, not removed by boiling. Sodium bicarbonate does not cause hardness. Methods to remove permanent hardness include treatment with washing soda (Na₂CO₃), ion exchange, or calgon.

This question belongs to: Science chemistry

Question #40

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The process of adding chlorine to water to kill bacteria is called:

A. Distillation

B. Filtration

C. Chlorination

D. Ozonation

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Correct Answer: Option C

Explanation:
Chlorination is the disinfection of water using chlorine or chlorine compounds to destroy pathogenic microorganisms. Chlorine reacts with water forming hypochlorous acid (HOCl) which is a strong germicide. Ozonation uses ozone; distillation involves boiling and condensation. Filtration removes particulate matter but not all microorganisms. Chlorination is cost-effective and provides residual protection, though it may produce trihalomethanes as by-products.

This question belongs to: Science chemistry

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