Chemistry MCQs

Question #501

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

A. Roasting

B. Smelting

C. Calcination

D. Leaching

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Correct Answer: Option A

Explanation:
Roasting involves heating sulfide ores in excess air to convert them to oxides and remove sulfur as SO₂. Example: 2ZnS + 3O₂ → 2ZnO + 2SO₂. Calcination is heating in absence of air (for carbonates/hydroxides). Smelting is reduction. Leaching uses chemicals.

This question belongs to: Science chemistry

Question #502

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Nitric acid is manufactured by:

A. Bayer process

B. Ostwald process

C. Contact process

D. Haber process

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Correct Answer: Option B

Explanation:
Ostwald process: ammonia is oxidized with air over Pt-Rh catalyst to NO, then NO₂, then absorbed in water to give HNO₃. Haber for NH₃, Contact for H₂SO₄, Bayer for alumina from bauxite.

This question belongs to: Science chemistry

Question #503

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The acid used in lead storage batteries is:

A. Hydrochloric acid

B. Sulphuric acid

C. Phosphoric acid

D. Nitric acid

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Correct Answer: Option B

Explanation:
Lead-acid batteries use dilute H₂SO₄ as electrolyte. The electrodes are Pb and PbO₂. During discharge, both plates form PbSO₄ and the acid concentration decreases. Recharging reverses the reaction.

This question belongs to: Science chemistry

Question #504

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Caustic soda is the common name for:

A. Potassium hydroxide

B. Sodium hydroxide

C. Sodium carbonate

D. Sodium bicarbonate

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Correct Answer: Option B

Explanation:
Caustic soda is NaOH (sodium hydroxide). It is a strong base used in soap, paper, and textile industries. Washing soda is Na₂CO₃, baking soda NaHCO₃. Caustic potash is KOH.

This question belongs to: Science chemistry

Question #505

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The conversion of ethanol to ethene requires:

A. Dehydration

B. Hydrogenation

C. Oxidation

D. Fermentation

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Correct Answer: Option A

Explanation:
Ethanol (C₂H₅OH) on heating with excess concentrated H₂SO₄ (dehydrating agent) at 170°C undergoes dehydration to give ethene (C₂H₄). This is an elimination reaction. Oxidation gives ethanoic acid; hydrogenation adds H₂; fermentation produces ethanol.

This question belongs to: Science chemistry

Question #506

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Which of the following is a thermosetting plastic?

A. Nylon

B. Polythene

C. Bakelite

D. PVC

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Correct Answer: Option C

Explanation:
Bakelite (phenol-formaldehyde resin) is thermosetting; once molded, it cannot be reshaped by heating. Polythene, nylon, PVC are thermoplastics, which can be repeatedly softened by heat.

This question belongs to: Science chemistry

Question #507

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The hardness of water that cannot be removed by boiling is called:

A. Temporary hardness

B. Permanent hardness

C. Alkalinity

D. Softness

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Correct Answer: Option B

Explanation:
Permanent hardness is due to dissolved sulfates and chlorides of calcium and magnesium. Boiling does not remove it. It requires chemical treatment (washing soda, ion exchange) or distillation. Temporary hardness (bicarbonates) is removed by boiling.

This question belongs to: Science chemistry

Question #508

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The disinfectant used in municipal water supply that provides residual protection is:

A. Boiling

B. UV radiation

C. Ozone

D. Chlorine

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Correct Answer: Option D

Explanation:
Chlorine leaves a residual in water, continuing to protect against recontamination in distribution pipes. Ozone and UV kill instantly but do not provide residual disinfection. Boiling is not used for municipal supply.

This question belongs to: Science chemistry

Question #509

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Global warming leads to:

A. Cooling of the Earth

B. Decrease in sea level

C. Climate change and rise in sea level

D. Reduction in CO₂ concentration

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Correct Answer: Option C

Explanation:
Global warming, caused by increased greenhouse gases, leads to melting of polar ice, thermal expansion of oceans, rise in sea level, and changes in weather patterns (climate change). It does not cool the Earth or decrease CO₂.

This question belongs to: Science chemistry

Question #510

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Which of the following is a radioactive isotope used in the treatment of cancer?

A. Cobalt-60

B. Sodium-23

C. Phosphorus-31

D. Carbon-12

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Correct Answer: Option A

Explanation:
Cobalt-60 emits gamma rays used in radiotherapy to destroy cancerous cells. Carbon-12 and sodium-23 are stable. Phosphorus-32 is radioactive but used as tracer, not for cancer therapy.

This question belongs to: Science chemistry

Question #511

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Who proposed the law of constant composition?

A. Rutherford

B. Dalton

C. Lavoisier

D. Proust

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Correct Answer: Option D

Explanation:
Joseph Proust proposed the law of definite proportions (constant composition) – a given compound always contains the same elements in the same proportion by mass. Dalton's theory explained it. Lavoisier gave law of conservation of mass. Rutherford discovered nucleus.

This question belongs to: Science chemistry

Question #512

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Which of the following represents a chemical change?

A. Rusting of iron

B. Dissolving sugar in water

C. Melting of ice

D. Sublimation of iodine

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Correct Answer: Option A

Explanation:
Rusting is a chemical change because iron reacts with atmospheric oxygen and moisture to form hydrated iron(III) oxide. This new compound possesses entirely different chemical properties from the original iron. The process involves the formation of new chemical bonds and cannot be easily reversed by simple physical methods.

This question belongs to: Science chemistry

Question #513

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The process of converting a solid directly into gas without passing through the liquid state is called:

A. Fusion

B. Sublimation

C. Evaporation

D. Condensation

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Correct Answer: Option B

Explanation:
Sublimation is the transition of a substance directly from the solid to the gas state without becoming an intermediate liquid. Condensation is gas to liquid, evaporation is liquid to gas at any temperature, and fusion is solid to liquid. Common examples include camphor, naphthalene, and dry ice.

This question belongs to: Science chemistry

Question #514

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Identify the correct statement regarding the physical properties of matter.

A. Gases have the highest density among the three states.

B. Solids have the maximum intermolecular space.

C. Gases cannot be compressed.

D. Liquids have a definite volume but no definite shape.

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Correct Answer: Option D

Explanation:
Liquids have a definite volume but take the shape of their container. Solids have the least intermolecular space and highest density. Gases have maximum intermolecular space and are highly compressible. This relates directly to the kinetic theory of matter, which describes particle arrangement and movement in different states.

This question belongs to: Science chemistry

Question #515

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Assertion (A): The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close. Reason (R): The kinetic energy of gas molecules is higher at higher temperatures.

A. A is true but R is false.

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

C. A is false but R is true.

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

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Correct Answer: Option B

Explanation:
At higher temperatures, the rate of diffusion increases because the kinetic energy of the gas molecules (food aroma) increases. Thus, the smell of hot food diffuses faster and reaches further. Both statements are correct, and the increased kinetic energy perfectly explains the enhanced diffusion rate observed in the assertion.

This question belongs to: Science chemistry

Question #516

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Which of the following sequences correctly represents the increasing order of forces of attraction between particles?

A. Oxygen, water, sugar

B. Water, sugar, oxygen

C. Sugar, water, oxygen

D. Oxygen, sugar, water

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Correct Answer: Option A

Explanation:
The forces of attraction are minimum in gases, intermediate in liquids, and maximum in solids. Oxygen is a gas, water is a liquid, and sugar is a solid. Thus, the increasing order of intermolecular forces is oxygen < water < sugar, reflecting their respective physical states at room temperature.

This question belongs to: Science chemistry

Question #517

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Latent heat of fusion is defined as the heat required to:

A. Change 1 kg of solid to liquid at its melting point.

B. Raise the temperature of 1 kg of solid by 1°C.

C. Change 1 kg of gas to liquid at its condensation point.

D. Change 1 kg of liquid to gas at its boiling point.

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Correct Answer: Option A

Explanation:
Latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure and its melting point, without any change in temperature. Option B describes latent heat of vaporization, while C describes specific heat capacity.

This question belongs to: Science chemistry

Question #518

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During the interconversion of states, which property remains constant?

A. Shape

B. Density

C. Volume

D. Mass

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Correct Answer: Option D

Explanation:
According to the law of conservation of mass, the mass of a substance remains constant during any physical change, including the interconversion of states. Density, volume, and shape change as the intermolecular spaces and arrangement alter during phase transitions, but the total number of atoms and mass is conserved.

This question belongs to: Science chemistry

Question #519

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Which of the following will cause an increase in the rate of evaporation of a liquid?

A. Decrease in temperature

B. Decrease in wind speed

C. Increase in surface area

D. Increase in humidity

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Correct Answer: Option C

Explanation:
Evaporation increases with an increase in surface area, temperature, and wind speed, and decreases with an increase in humidity. A larger surface area allows more liquid molecules to be exposed to the air, enabling them to escape into the vapor phase more quickly, thus increasing the rate of evaporation.

This question belongs to: Science chemistry

Question #520

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A substance has a melting point of -10°C and a boiling point of 50°C. At room temperature (25°C), it exists in which state?

A. Gas

B. Solid

C. Plasma

D. Liquid

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Correct Answer: Option D

Explanation:
Since the room temperature (25°C) is between its melting point (-10°C) and boiling point (50°C), the substance exists in the liquid state. If the temperature were below -10°C, it would be solid, and above 50°C, it would be gas. This is based on standard phase transition principles.

This question belongs to: Science chemistry

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