Chemistry MCQs

Question #601

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An ideal gas is one that:

A. Obeys all gas laws perfectly at all temperatures and pressures.

B. Has no mass.

C. Cannot be liquefied.

D. Both B and C

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Correct Answer: Option D

Explanation:
An ideal gas is a theoretical gas that perfectly obeys the ideal gas equation (PV=nRT) and all gas laws under all conditions. It assumes no intermolecular forces and zero molecular volume. Because of these assumptions, an ideal gas cannot be liquefied, unlike real gases which deviate at high pressures.

This question belongs to: Science chemistry

Question #602

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The rate of diffusion of a gas is:

A. Independent of its density.

B. Directly proportional to the square root of its density.

C. Directly proportional to its density.

D. Inversely proportional to the square root of its density.

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Correct Answer: Option D

Explanation:
Graham's Law of Diffusion states that the rate of diffusion of a gas is inversely proportional to the square root of its density (or molar mass) at constant temperature and pressure (r ∝ 1/√d). Lighter gases diffuse faster than heavier ones, which explains why helium balloons deflate quickly.

This question belongs to: Science chemistry

Question #603

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If the volume of a gas is doubled at constant temperature, its pressure will:

A. Become four times

B. Halve

C. Remain the same

D. Double

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Correct Answer: Option B

Explanation:
According to Boyle's Law (P₁V₁ = P₂V₂), pressure and volume are inversely proportional at constant temperature. If the volume is doubled (V₂ = 2V₁), the pressure must be halved (P₂ = P₁/2) to keep the product constant. This demonstrates the inverse relationship between P and V.

This question belongs to: Science chemistry

Question #604

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The value of the universal gas constant 'R' in SI units is:

A. 8.314 L·atm/(mol·K)

B. 8.314 J/(mol·K)

C. 0.0821 L·atm/(mol·K)

D. 1.987 cal/(mol·K)

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Correct Answer: Option B

Explanation:
The universal gas constant R has different values depending on the units used. In SI units (Joules), R = 8.314 J/(mol·K). In L·atm, it is 0.0821 L·atm/(mol·K). Option D mixes SI and L·atm units incorrectly. The value of R is fundamental in thermodynamic calculations.

This question belongs to: Science chemistry

Question #605

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Which of the following gases will diffuse the fastest?

A. Hydrogen (H₂)

B. Oxygen (O₂)

C. Carbon dioxide (CO₂)

D. Nitrogen (N₂)

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Correct Answer: Option A

Explanation:
According to Graham's law, the rate of diffusion is inversely proportional to the square root of molar mass. Hydrogen (H₂) has the lowest molar mass (2 g/mol) among the options (O₂=32, N₂=28, CO₂=44), so it will diffuse the fastest under identical conditions of temperature and pressure.

This question belongs to: Science chemistry

Question #606

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A catalyst is a substance that:

A. Increases the activation energy of a reaction.

B. Is completely consumed in the reaction.

C. Changes the equilibrium constant of a reaction.

D. Alters the rate of a chemical reaction without being consumed.

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Correct Answer: Option D

Explanation:
A catalyst speeds up (positive catalyst) or slows down (negative catalyst) a chemical reaction by providing an alternative pathway with a lower (or higher) activation energy. It remains chemically unchanged and in the same amount at the end of the reaction, and does not alter the equilibrium position.

This question belongs to: Science chemistry

Question #607

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Enzymes are biological catalysts that are:

A. Mostly carbohydrates

B. Mostly proteins

C. Mostly nucleic acids

D. Mostly lipids

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Correct Answer: Option B

Explanation:
Enzymes are complex organic molecules that act as biological catalysts in living organisms. Chemically, most enzymes are globular proteins. They are highly specific to their substrates and work optimally at body temperature and near-neutral pH, unlike many industrial catalysts that require extreme conditions.

This question belongs to: Science chemistry

Question #608

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In the Haber process for the manufacture of ammonia, the catalyst used is:

A. Nickel (Ni)

B. Platinum (Pt)

C. Finely divided Iron (Fe)

D. Vanadium pentoxide (V₂O₅)

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Correct Answer: Option C

Explanation:
The Haber process synthesizes ammonia from nitrogen and hydrogen (N₂ + 3H₂ ⇌ 2NH₃). Finely divided iron acts as the catalyst, often with molybdenum as a promoter, to increase the rate of reaction at high pressure and moderate temperature. V₂O₅ is used in the Contact process.

This question belongs to: Science chemistry

Question #609

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Which of the following statements about a catalyst is incorrect?

A. It lowers the activation energy.

B. It initiates the reaction.

C. It remains unchanged in mass after the reaction.

D. It does not change the enthalpy of the reaction.

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Correct Answer: Option B

Explanation:
A catalyst does not initiate a reaction; it only changes the rate of a reaction that is already thermodynamically feasible. It provides an alternative pathway with lower activation energy. It does not change the overall enthalpy (ΔH) or the equilibrium position, and it is recovered unchanged in mass.

This question belongs to: Science chemistry

Question #610

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The catalyst used in the Contact process for manufacturing sulfuric acid is:

A. Manganese dioxide

B. Iron

C. Nickel

D. Vanadium pentoxide (V₂O₅)

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Correct Answer: Option D

Explanation:
The Contact process involves the oxidation of SO₂ to SO₃. The catalyst used for this step is Vanadium pentoxide (V₂O₅) or sometimes platinized asbestos. Iron is used in the Haber process, and Nickel is commonly used in the hydrogenation of vegetable oils.

This question belongs to: Science chemistry

Question #611

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Assertion (A): A catalyst does not change the equilibrium yield of a reaction. Reason (R): A catalyst speeds up both the forward and backward reactions equally.

A. A is true but R is false.

B. A is false but R is true.

C. Both A and R are true but R is NOT the correct explanation of A.

D. Both A and R are true and R is the correct explanation of A.

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Correct Answer: Option D

Explanation:
A catalyst lowers the activation energy for both the forward and reverse reactions by the same amount. Therefore, it increases the rates of both reactions equally, allowing the system to reach equilibrium faster, but without changing the final equilibrium concentrations (yield). Both statements are correct and R explains A.

This question belongs to: Science chemistry

Question #612

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Which of the following is an example of an enzyme catalyst?

A. Zymase

B. All of the above

C. Catalase

D. Amylase

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Correct Answer: Option B

Explanation:
Zymase (in yeast) converts sugars to ethanol, catalase (in liver) breaks down hydrogen peroxide, and amylase (in saliva) breaks down starch into sugars. All are biological enzymes that act as highly specific catalysts in biochemical reactions, functioning under mild conditions of temperature and pH.

This question belongs to: Science chemistry

Question #613

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The substance that increases the efficiency of a catalyst is called a:

A. Promoter

B. Reactant

C. Inhibitor

D. Poison

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Correct Answer: Option A

Explanation:
A promoter is a substance that, when added in small quantities, enhances the activity or efficiency of a catalyst. For example, in the Haber process, molybdenum acts as a promoter for the iron catalyst. An inhibitor or poison decreases catalyst activity by blocking active sites.

This question belongs to: Science chemistry

Question #614

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Catalytic converters in automobiles use which metals to reduce pollution?

A. Gold, Silver, Copper

B. Platinum, Palladium, Rhodium

C. Zinc, Lead, Tin

D. Iron, Copper, Nickel

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Correct Answer: Option B

Explanation:
Catalytic converters use precious metals like platinum, palladium, and rhodium as catalysts to convert toxic exhaust gases (CO, NOx, unburnt hydrocarbons) into less harmful substances (CO₂, N₂, H₂O) before they are released into the atmosphere. These metals are chosen for their high catalytic activity and durability.

This question belongs to: Science chemistry

Question #615

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The scientific process of extracting a metal from its ore and refining it is called:

A. Metallurgy

B. Agriculture

C. Geology

D. Mineralogy

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Correct Answer: Option A

Explanation:
Metallurgy is the science and technology of extracting metals from their ores, purifying them, and preparing them for use. It involves various steps like concentration, reduction, and refining. Mineralogy is the study of minerals, and geology is the study of the Earth's physical structure.

This question belongs to: Science chemistry

Question #616

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Which of the following is an ore of aluminum?

A. Bauxite

B. Haematite

C. Galena

D. Cinnabar

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Correct Answer: Option A

Explanation:
Bauxite (Al₂O₃·2H₂O) is the primary ore of aluminum. Haematite (Fe₂O₃) is an ore of iron. Cinnabar (HgS) is an ore of mercury, and Galena (PbS) is an ore of lead. Bauxite is purified to alumina before being electrolyzed to extract pure aluminum metal.

This question belongs to: Science chemistry

Question #617

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The process of heating an ore strongly in the absence of air is called:

A. Leaching

B. Roasting

C. Calcination

D. Smelting

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Correct Answer: Option C

Explanation:
Calcination is the process of heating a concentrated ore strongly in the absence or limited supply of air. It is typically used for carbonate ores to drive off volatile impurities like CO₂ and H₂O (e.g., CaCO₃ → CaO + CO₂). Roasting is done in the presence of excess air.

This question belongs to: Science chemistry

Question #618

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In the thermite reaction, aluminum is used to reduce:

A. Zinc oxide

B. Lead oxide

C. Iron oxide

D. Copper oxide

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Correct Answer: Option C

Explanation:
The thermite reaction involves aluminum powder reacting with iron(III) oxide to produce molten iron and aluminum oxide (2Al + Fe₂O₃ → Al₂O₃ + 2Fe). It is highly exothermic and is used for welding railway tracks and repairing metal structures in the field.

This question belongs to: Science chemistry

Question #619

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Which method is used for the concentration of an ore based on the difference in density between the ore and impurities?

A. Leaching

B. Magnetic separation

C. Hydraulic washing

D. Froth flotation

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Correct Answer: Option C

Explanation:
Hydraulic washing (or gravity separation) is based on the difference in specific gravities (densities) of the ore and the gangue (impurities). The powdered ore is washed with a stream of water; lighter impurities are washed away, leaving the heavier ore particles behind.

This question belongs to: Science chemistry

Question #620

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The process of converting a concentrated ore into its oxide by heating in excess air is:

A. Refining

B. Roasting

C. Smelting

D. Calcination

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Correct Answer: Option B

Explanation:
Roasting is the process of heating the concentrated ore (usually sulfide ores) strongly in the presence of excess air below its melting point. It converts the ore to its oxide form and removes volatile impurities as gases (e.g., 2ZnS + 3O₂ → 2ZnO + 2SO₂).

This question belongs to: Science chemistry

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