Chemistry MCQs

Question #321

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Ionization energy is the energy required to:

A. Add an electron to a gaseous atom

B. Break a covalent bond

C. Form an ionic crystal

D. Remove the most loosely held electron from a gaseous atom

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Correct Answer: Option D

Explanation:
Ionization energy (IE) is the minimum energy needed to remove an electron from an isolated gaseous atom in its ground state to form a cation. A(g) → A⁺(g) + e⁻. Adding an electron is electron affinity. IE is an indicator of reactivity. Metals have low IE, non-metals high IE.

This question belongs to: Science chemistry

Question #322

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The reaction 2H₂O₂ → 2H₂O + O₂ is a:

A. Displacement reaction

B. Combination reaction

C. Decomposition reaction

D. Double displacement reaction

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Correct Answer: Option C

Explanation:
Hydrogen peroxide decomposes into water and oxygen. A single reactant breaks down into two or more products, so it is a decomposition reaction. This particular reaction can be catalyzed by MnO₂ or light. It is also a disproportionation redox reaction where O in H₂O₂ (-1) goes to -2 in H₂O and 0 in O₂.

This question belongs to: Science chemistry

Question #323

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Which of the following is an example of oxidation?

A. Cl₂ + 2e⁻ → 2Cl⁻

B. Na → Na⁺ + e⁻

C. 2H⁺ + 2e⁻ → H₂

D. Cu²⁺ + 2e⁻ → Cu

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Correct Answer: Option B

Explanation:
Oxidation is loss of electrons. Na loses an electron to become Na⁺, so it is oxidized. Options A, C, D involve gain of electrons (reduction). Oxidation also can be defined as gain of oxygen or loss of hydrogen. In the reaction, Na acts as reducing agent. Mnemonic: LEO (Loss of Electrons is Oxidation) GER (Gain of Electrons is Reduction).

This question belongs to: Science chemistry

Question #324

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A solution with pH 1 is more acidic than a solution with pH 4 by a factor of:

A. 100

B. 1000

C. 30

D. 3

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Correct Answer: Option B

Explanation:
Difference in pH = 3. Each pH unit is a 10-fold change in [H⁺]. So 10³ = 1000 times more acidic. [H⁺] at pH 1 = 10⁻¹ M, at pH 4 = 10⁻⁴ M. Ratio = 10⁻¹ / 10⁻⁴ = 10³ = 1000. pH scale is logarithmic; small changes mean large concentration differences.

This question belongs to: Science chemistry

Question #325

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Bleaching powder (CaOCl₂) releases chlorine when treated with:

A. Water only

B. Ammonia

C. Sodium hydroxide

D. Dilute acids

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Correct Answer: Option D

Explanation:
CaOCl₂ + 2HCl (dil.) → CaCl₂ + Cl₂ + H₂O. It also releases Cl₂ on reaction with CO₂ in air: CaOCl₂ + CO₂ → CaCO₃ + Cl₂. Water alone hydrolyses it slowly. NaOH does not release Cl₂. The chlorine gas is responsible for bleaching and disinfection.

This question belongs to: Science chemistry

Question #326

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Which metal is used in the thermite process for welding railway tracks?

A. Copper

B. Aluminium

C. Iron

D. Zinc

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Correct Answer: Option B

Explanation:
Thermite process uses a mixture of aluminium powder and iron(III) oxide: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat. The reaction is highly exothermic, producing molten iron that is used to join railway tracks. Aluminium acts as a reducing agent. Copper, zinc, iron are not used as the reducing agent in this process.

This question belongs to: Science chemistry

Question #327

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Corrosion of iron is an electrochemical process that requires:

A. Only high temperature

B. Only nitrogen

C. An electrolyte, oxygen, and water

D. Only CO₂

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Correct Answer: Option C

Explanation:
Rusting involves anodic oxidation of iron (Fe → Fe²⁺ + 2e⁻) and cathodic reduction of oxygen (O₂ + 2H₂O + 4e⁻ → 4OH⁻) in the presence of water acting as electrolyte. CO₂ can form carbonic acid accelerating it, but not required. Nitrogen is inert. High temperature alone doesn't cause rusting without moisture and oxygen.

This question belongs to: Science chemistry

Question #328

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Diamond has a high melting point because:

A. It has strong covalent network bonds throughout the crystal

B. It has weak bonds

C. It is made of carbon

D. It has free electrons

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Correct Answer: Option A

Explanation:
Diamond is a giant covalent structure where each carbon is tetrahedrally bonded to four others via strong covalent bonds. Melting requires breaking numerous strong bonds, needing very high temperature (~3500°C). Graphite also has high melting point. Molecular solids like ice have low melting points. Carbon alone doesn't guarantee high m.p.; it's the structure.

This question belongs to: Science chemistry

Question #329

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Which of the following hydrocarbons is an unsaturated compound?

A. C₅H₁₂

B. C₃H₈

C. C₄H₁₀

D. C₂H₄

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Correct Answer: Option D

Explanation:
C₂H₄ (ethene) is an alkene with a carbon-carbon double bond, thus unsaturated. The general formula CnH₂n indicates an alkene or cycloalkane. C₃H₈, C₄H₁₀, C₅H₁₂ follow CnH₂n+2 and are saturated alkanes. Unsaturated compounds undergo addition reactions, whereas saturated undergo substitution.

This question belongs to: Science chemistry

Question #330

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The process of separating petroleum into various fractions is called:

A. Refining

B. Cracking

C. Polymerisation

D. Fractional distillation

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Correct Answer: Option D

Explanation:
Fractional distillation is the primary separation method in a petroleum refinery, where crude oil is heated and components separated based on boiling points. Cracking breaks larger molecules into smaller ones. Refining includes many processes including distillation. Polymerisation is joining molecules. Fractional distillation yields petrol, kerosene, diesel, etc.

This question belongs to: Science chemistry

Question #331

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During electrolysis, the amount of substance deposited depends on the quantity of electricity passed. This is:

A. Graham's law

B. Faraday's second law

C. Faraday's first law

D. Ohm's law

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Correct Answer: Option C

Explanation:
Faraday's first law of electrolysis: Mass of substance deposited or liberated is proportional to the charge passed (m = ZQ). Z is electrochemical equivalent. Second law relates masses of different substances to equivalent weights for same charge. Ohm's law is V=IR, Graham's law for diffusion. Faraday's laws are quantitative.

This question belongs to: Science chemistry

Question #332

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A gas occupies 500 mL at 27°C. What will be its volume at 0°C at constant pressure?

A. 550 mL

B. 600 mL

C. 0 mL

D. 455 mL

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Correct Answer: Option D

Explanation:
Charles' law: V₁/T₁ = V₂/T₂. T₁ = 27+273=300 K, V₁=500 mL; T₂ = 0+273=273 K. V₂ = V₁ × T₂/T₁ = 500 × 273/300 = 500 × 0.91 = 455 mL. Volume decreases as temperature decreases. At absolute zero, volume would be zero theoretically.

This question belongs to: Science chemistry

Question #333

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Which of the following statements about catalysts is correct?

A. They lower the activation energy of the reaction

B. They are always solid

C. They change the equilibrium constant

D. They are consumed in the reaction

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Correct Answer: Option A

Explanation:
Catalysts provide an alternative pathway with lower activation energy, increasing reaction rate without being consumed. They do not affect equilibrium constant or thermodynamic parameters (ΔH, ΔS). They can be solid (heterogeneous), liquid, or gas. Enzymes are liquid-phase catalysts. A catalyst does not change the position of equilibrium, only speeds up attainment.

This question belongs to: Science chemistry

Question #334

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Enzyme catalase decomposes hydrogen peroxide in cells. This enzyme is present in:

A. Muscles only

B. Stomach

C. Bones

D. Liver and red blood cells

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Correct Answer: Option D

Explanation:
Catalase is an enzyme found in nearly all living organisms, particularly high in liver and red blood cells. It catalyzes the decomposition of toxic hydrogen peroxide to water and oxygen: 2H₂O₂ → 2H₂O + O₂. This protects cells from oxidative damage. It has one of the highest turnover numbers. Stomach has pepsin.

This question belongs to: Science chemistry

Question #335

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Which of the following metals is obtained by the reduction of its oxide by aluminium?

A. Iron

B. Manganese

C. Zinc

D. Sodium

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Correct Answer: Option B

Explanation:
Manganese is extracted by the aluminothermic process (Goldschmidt thermite process) where Mn₃O₄ is reduced by aluminium: 3Mn₃O₄ + 8Al → 9Mn + 4Al₂O₃. This works for metals with less reactivity than Al but not too reactive. Sodium is extracted by electrolysis. Iron is extracted by smelting with coke. Zinc by carbon reduction/electrolysis.

This question belongs to: Science chemistry

Question #336

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Which of the following is a mixed fertilizer?

A. Ammonium sulfate

B. NPK

C. Urea

D. Superphosphate

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Correct Answer: Option B

Explanation:
NPK is a mixed (complex) fertilizer containing nitrogen, phosphorus, and potassium. Urea is a straight nitrogenous fertilizer. Ammonium sulfate is nitrogenous. Superphosphate is phosphatic. Mixed fertilizers supply two or more primary nutrients. They can be granulated or blended. DAP provides N and P, but NPK provides all three.

This question belongs to: Science chemistry

Question #337

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Sulphuric acid is produced by Contact process. The raw materials are:

A. NH₃, air, water

B. CaCO₃, HCl

C. S or FeS₂, air, water

D. NaCl, H₂O

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Correct Answer: Option C

Explanation:
Contact process: Sulfur or pyrite (FeS₂) is burned in air to form SO₂, then SO₂ is oxidized with O₂ over V₂O₅ catalyst to SO₃, which is absorbed in concentrated H₂SO₄ to produce oleum, then diluted to get H₂SO₄. Raw materials: sulfur (or pyrite), air, and water (for dilution). Not NaCl or NH₃.

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Question #338

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Which acid is used in the manufacture of explosives like TNT and nitroglycerin?

A. HCl

B. H₂SO₄

C. CH₃COOH

D. HNO₃

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Correct Answer: Option D

Explanation:
Nitric acid (HNO₃) is used for nitration reactions to produce explosives such as TNT (trinitrotoluene), nitroglycerin, and dynamite. Sulfuric acid acts as a catalyst/dehydrating agent in nitration mixtures (mixed acid). HCl is used for cleaning and chemical synthesis. Acetic acid is organic acid. Nitric acid provides nitro groups (-NO₂).

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Question #339

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Sodium hydroxide (NaOH) is prepared industrially by the electrolysis of brine. The by-product chlorine is used in:

A. Fertilizer production

B. Steel making

C. PVC and disinfectants

D. Glass manufacturing

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Correct Answer: Option C

Explanation:
Chlorine produced in the chlor-alkali process is used to manufacture PVC (polyvinyl chloride), bleaching powder, disinfectants, and solvents. Glass uses Na₂CO₃. Fertilizers use NH₃ and acids. Steel making uses oxygen. Chlorine is a versatile industrial chemical with many downstream products.

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Question #340

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Hydrogen peroxide is used as an antiseptic because it:

A. Reduces bacteria

B. Oxidizes bacterial cell components

C. Dehydrates cells

D. Is a strong acid

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Correct Answer: Option B

Explanation:
H₂O₂ is a strong oxidizing agent that damages bacterial cell walls, membranes, and essential biomolecules through oxidation, killing microorganisms. It is used as a 3% solution for wound cleaning. The foaming action is due to catalase in tissues breaking it down, releasing O₂. It is not a reducing agent, acid, or dehydrating agent.

This question belongs to: Science chemistry

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