Chemistry MCQs

Question #821

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In the redox reaction Zn + CuSO₄ → ZnSO₄ + Cu, the reducing agent is:

A. ZnSO₄

B. Cu

C. CuSO₄

D. Zn

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Correct Answer: Option D

Explanation:
Zinc loses electrons (Zn → Zn²⁺ + 2e⁻) and thus is oxidized. The substance that gets oxidized is the reducing agent. Copper sulfate is reduced (Cu²⁺ to Cu) and is the oxidizing agent. The reducing agent donates electrons.

This question belongs to: Science chemistry

Question #822

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Which of the following statements about oxidation is correct?

A. It always involves oxygen.

B. It involves decrease in oxidation number.

C. It involves gain of electrons.

D. It involves loss of electrons.

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Correct Answer: Option D

Explanation:
Oxidation is defined as loss of electrons, increase in oxidation number, or loss of hydrogen / gain of oxygen. Reduction is gain of electrons. Oxidation does not always require oxygen; for example, 2Na + Cl₂ → 2NaCl involves oxidation of Na without oxygen.

This question belongs to: Science chemistry

Question #823

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A solution with a pH of 2 is how many times more acidic than a solution with a pH of 5?

A. 1000 times

B. 3 times

C. 100 times

D. 10 times

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Correct Answer: Option A

Explanation:
pH difference = 3 units. Since pH is logarithmic (base 10), [H⁺] ratio = 10³ = 1000. So pH 2 solution has 1000 times greater H⁺ concentration, making it 1000 times more acidic.

This question belongs to: Science chemistry

Question #824

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Which metal is the most reactive among the following?

A. Cu

B. Fe

C. Na

D. Zn

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Correct Answer: Option C

Explanation:
Reactivity series order: Na > Zn > Fe > Cu. Sodium (alkali metal) is extremely reactive, reacting violently with water. Copper is low in the series, hence used for water pipes.

This question belongs to: Science chemistry

Question #825

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Rusting of iron is prevented by galvanization, which is the coating of iron with:

A. Zinc

B. Nickel

C. Chromium

D. Tin

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Correct Answer: Option A

Explanation:
Galvanization involves coating iron with zinc. Zinc acts as a sacrificial anode, corroding in preference to iron even if the coating is scratched. Tin plating (tin cans) only protects if the layer is intact.

This question belongs to: Science chemistry

Question #826

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Diamond is not a good conductor of electricity because:

A. All valence electrons are involved in covalent bonds.

B. It has a layered structure.

C. It is very hard.

D. It is made of carbon.

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Correct Answer: Option A

Explanation:
In diamond, each carbon atom is sp³ hybridized and forms four strong covalent bonds, utilizing all four valence electrons. No free electrons are available for conduction. Graphite has free delocalized electrons per carbon, making it a conductor.

This question belongs to: Science chemistry

Question #827

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Which hydrocarbon belongs to the alkene series?

A. C₂H₆

B. C₃H₈

C. CH₄

D. C₂H₄

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Correct Answer: Option D

Explanation:
Alkenes follow CₙH₂ₙ. C₂H₄ (ethene) fits n=2 giving H=4. C₂H₆ and CH₄ are alkanes (CₙH₂ₙ₊₂); C₃H₈ is propane (alkane). Alkenes contain a carbon-carbon double bond.

This question belongs to: Science chemistry

Question #828

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Which of the following fuels has the highest calorific value?

A. Hydrogen

B. Coal

C. Cow dung cake

D. Petrol

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Correct Answer: Option A

Explanation:
Hydrogen has about 150 kJ/g (highest). Petrol ~47 kJ/g, coal ~25-35 kJ/g, cow dung cake ~8 kJ/g. Hydrogen produces only water on combustion and is a clean fuel.

This question belongs to: Science chemistry

Question #829

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During electrolysis, reduction occurs at the:

A. Cathode

B. Salt bridge

C. Anode

D. Electrolyte

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Correct Answer: Option A

Explanation:
Cathode is where reduction (gain of electrons) takes place in both electrolytic and galvanic cells. Anode is where oxidation occurs. Mnemonic: RED CAT (Reduction at Cathode), AN OX (Oxidation at Anode).

This question belongs to: Science chemistry

Question #830

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Boyle's law states that at constant temperature, the pressure of a gas is inversely proportional to its:

A. Volume

B. Mass

C. Temperature

D. Density

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Correct Answer: Option A

Explanation:
Boyle's law: PV = constant (at fixed T and n). So P ∝ 1/V. If volume is doubled, pressure halves. Charles' law relates V and T; Graham's law relates diffusion rate to molar mass.

This question belongs to: Science chemistry

Question #831

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Which catalyst is used in the hydrogenation of unsaturated vegetable oils?

A. Nickel

B. Platinum

C. Vanadium pentoxide

D. Iron

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Correct Answer: Option A

Explanation:
Finely divided nickel catalyzes the addition of hydrogen to liquid oils to form solid fats (vanaspati ghee). Platinum/palladium also work but are expensive. Iron is used in Haber process; V₂O₅ in Contact process.

This question belongs to: Science chemistry

Question #832

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Enzymes are biological catalysts. Which statement about them is correct?

A. They are consumed during the reaction.

B. They work optimally at very high temperatures.

C. They are inorganic compounds.

D. They are highly specific in their action.

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Correct Answer: Option D

Explanation:
Enzymes are proteins that act as catalysts, exhibiting high specificity for substrates (lock-and-key model). They are not consumed, denature at high temperatures, and are organic. Examples: amylase for starch, pepsin for proteins.

This question belongs to: Science chemistry

Question #833

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The chief ore of iron is:

A. Bauxite

B. Haematite

C. Cinnabar

D. Galena

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Correct Answer: Option B

Explanation:
Haematite (Fe₂O₃) is a major ore of iron. Bauxite is aluminium ore, galena is lead sulfide, cinnabar is mercury sulfide. Magnetite (Fe₃O₄) is another iron ore.

This question belongs to: Science chemistry

Question #834

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Which fertilizer contains the highest percentage of nitrogen?

A. Sodium nitrate

B. Urea

C. Ammonium sulfate

D. DAP

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Correct Answer: Option B

Explanation:
Urea (NH₂CONH₂) contains about 46% N. Ammonium sulfate ~21% N, sodium nitrate ~16% N, DAP ~18% N (and 46% P₂O₅). Urea is the most concentrated solid nitrogen fertilizer.

This question belongs to: Science chemistry

Question #835

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Sulphuric acid is known as:

A. Muriatic acid

B. Aqua fortis

C. Carbolic acid

D. Oil of vitriol

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Correct Answer: Option D

Explanation:
Sulphuric acid (H₂SO₄) was historically called oil of vitriol. Hydrochloric acid was muriatic acid, nitric acid was aqua fortis, carbolic acid is phenol.

This question belongs to: Science chemistry

Question #836

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Which gas is evolved when sodium bicarbonate is heated?

A. Carbon dioxide

B. Nitrogen

C. Hydrogen

D. Oxygen

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Correct Answer: Option A

Explanation:
2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O. Carbon dioxide is released, which turns limewater milky. This is a test for bicarbonates. Oxygen is not produced; hydrogen would need a reducing agent.

This question belongs to: Science chemistry

Question #837

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The chemical used as an antacid is:

A. Sodium bicarbonate

B. Sodium hydroxide

C. Sodium chloride

D. Calcium sulfate

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Correct Answer: Option A

Explanation:
Sodium bicarbonate (NaHCO₃) neutralizes excess stomach acid (HCl) and provides relief from acidity. It is a mild base. NaOH is too strong and corrosive. NaCl is table salt; CaSO₄ is used in plaster of Paris.

This question belongs to: Science chemistry

Question #838

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Which of the following methods is used to obtain pure copper from impure copper?

A. Roasting

B. Smelting

C. Calcination

D. Electrolytic refining

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Correct Answer: Option D

Explanation:
In electrolytic refining, impure copper is the anode, pure copper is the cathode, and CuSO₄ acidified with H₂SO₄ is the electrolyte. Copper dissolves from anode and pure copper deposits on cathode. Smelting is reduction with coke.

This question belongs to: Science chemistry

Question #839

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The chemical formula of plaster of Paris is:

A. CaSO₄·½H₂O

B. CaO

C. CaSO₄·2H₂O

D. CaSO₄

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Correct Answer: Option A

Explanation:
Plaster of Paris is calcium sulfate hemihydrate, CaSO₄·½H₂O. It is prepared by heating gypsum (CaSO₄·2H₂O) at 373 K. It sets with water to form gypsum.

This question belongs to: Science chemistry

Question #840

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Identify the correct statement regarding graphite:

A. It has a layered structure and conducts electricity.

B. It is a form of coal.

C. It is an electrical insulator.

D. It is the hardest natural substance.

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Correct Answer: Option A

Explanation:
Graphite has a layered structure with weak van der Waals forces between layers and delocalized electrons within layers, making it a good conductor and lubricant. Diamond is the hardest; coal is amorphous carbon.

This question belongs to: Science chemistry

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