Chemistry MCQs

Question #841

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The hydrocarbon C₄H₁₀ is named:

A. Butane

B. Pentane

C. Propane

D. Ethane

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Correct Answer: Option A

Explanation:
C₄H₁₀ is butane (n-butane or isobutane). Methane (CH₄), ethane (C₂H₆), propane (C₃H₈). It is used as LPG component.

This question belongs to: Science chemistry

Question #842

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The unit of electrochemical equivalent (Z) is:

A. g/mol

B. C/g

C. C/mol

D. g/C (gram per coulomb)

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Correct Answer: Option D

Explanation:
From Faraday's first law, m = ZQ, so Z = m/Q. SI unit is kg/C, but practical unit is g/C. It is the mass of substance liberated per unit charge.

This question belongs to: Science chemistry

Question #843

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A gas occupies 300 mL at 27°C. At constant pressure, what will be the volume at 0°C?

A. 273 mL

B. 327 mL

C. 300 mL

D. 250 mL

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Correct Answer: Option A

Explanation:
Charles' law: V₁/T₁ = V₂/T₂. T₁ = 300 K (27+273), V₁=300 mL; T₂=273 K. V₂ = 300 × (273/300) = 273 mL. Volume decreases as temperature decreases.

This question belongs to: Science chemistry

Question #844

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Which of the following gases diffuses fastest under identical conditions?

A. NH₃

B. O₂

C. Cl₂

D. N₂

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Correct Answer: Option A

Explanation:
Graham's law: rate ∝ 1/√M. Molar masses: O₂=32, N₂=28, NH₃=17, Cl₂=71. NH₃ has the smallest molar mass, so it diffuses fastest.

This question belongs to: Science chemistry

Question #845

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An enzyme that digests proteins in the stomach is:

A. Pepsin

B. Amylase

C. Ptyalin

D. Lipase

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Correct Answer: Option A

Explanation:
Pepsin is a protease secreted in the stomach; it hydrolyzes proteins into peptides. Ptyalin (salivary amylase) digests starch; amylase also breaks starch; lipase digests fats.

This question belongs to: Science chemistry

Question #846

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The process of removing gangue from ores by using water and oil is:

A. Magnetic separation

B. Calcination

C. Leaching

D. Froth flotation

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Correct Answer: Option D

Explanation:
Froth flotation separates sulfide ores: powdered ore mixed with water and pine oil; air bubbles carry oil-wetted ore particles to surface as froth; gangue sinks. Used for ZnS, PbS.

This question belongs to: Science chemistry

Question #847

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Ammonia gas is manufactured by the Haber process. The catalyst employed is:

A. V₂O₅

B. Ni

C. Pt

D. Fe

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Correct Answer: Option D

Explanation:
Haber process: N₂ + 3H₂ ⇌ 2NH₃, conditions: 400-450°C, 200 atm, finely divided iron with promoters (K₂O, Al₂O₃). Pt is used in Ostwald process for HNO₃; V₂O₅ in Contact process for H₂SO₄.

This question belongs to: Science chemistry

Question #848

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Which of the following is an example of a strong base?

A. Mg(OH)₂

B. NaOH

C. Ca(OH)₂ (slightly soluble)

D. NH₄OH

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Correct Answer: Option B

Explanation:
NaOH is a strong base, fully dissociating into Na⁺ and OH⁻ ions. NH₄OH is a weak base. Ca(OH)₂ and Mg(OH)₂ are sparingly soluble but are considered strong bases in terms of dissociation of dissolved portion, but NaOH is the strongest among common ones.

This question belongs to: Science chemistry

Question #849

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The product formed when ethanol reacts with ethanoic acid in presence of concentrated H₂SO₄ is:

A. Ethyl ethanoate

B. Ethane

C. Methanol

D. Ethene

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Correct Answer: Option A

Explanation:
C₂H₅OH + CH₃COOH ⇌ CH₃COOC₂H₅ + H₂O (esterification). Conc. H₂SO₄ acts as catalyst and dehydrating agent. Ethyl ethanoate is an ester with fruity smell.

This question belongs to: Science chemistry

Question #850

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Soaps are sodium salts of long-chain fatty acids. Which part of soap dissolves in grease?

A. Water molecule

B. Sodium ion

C. Hydrocarbon tail

D. Ionic head

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Correct Answer: Option C

Explanation:
The long non-polar hydrocarbon tail is hydrophobic and dissolves in grease/oil. The ionic head (carboxylate) is hydrophilic and interacts with water. This dual nature enables micelle formation and cleaning.

This question belongs to: Science chemistry

Question #851

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Glass is an amorphous solid. Which of the following properties is consistent with this?

A. High electrical conductivity

B. Sharp melting point

C. Long-range order

D. Gradual softening on heating

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Correct Answer: Option D

Explanation:
Amorphous solids like glass do not have a sharp melting point; they soften over a range of temperatures. Crystalline solids have sharp melting points and long-range order. Glass is an insulator.

This question belongs to: Science chemistry

Question #852

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The monomer of polyvinyl chloride (PVC) is:

A. Tetrafluoroethene

B. Styrene

C. Ethene

D. Vinyl chloride

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Correct Answer: Option D

Explanation:
PVC is made by addition polymerization of vinyl chloride (CH₂=CHCl). Ethene gives polythene, styrene gives polystyrene, tetrafluoroethene gives Teflon.

This question belongs to: Science chemistry

Question #853

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Temporary hardness of water is caused by bicarbonates. Boiling removes it by converting bicarbonates to:

A. Sulfates

B. Chlorides

C. Nitrates

D. Insoluble carbonates

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Correct Answer: Option D

Explanation:
Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂ (on boiling). The precipitate is calcium carbonate. Sulfates and chlorides cause permanent hardness and cannot be removed by boiling.

This question belongs to: Science chemistry

Question #854

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The disinfection method that leaves no residual effect in water is:

A. Chlorination

B. Chloramine treatment

C. Ozonation

D. Bleaching powder

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Correct Answer: Option C

Explanation:
Ozone decomposes quickly to O₂, leaving no residual disinfectant. Thus a small chlorine dose may be added after ozonation for distribution protection. Chlorine provides residual protection.

This question belongs to: Science chemistry

Question #855

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Acid rain is primarily caused by:

A. SO₂ and NOₓ

B. CO₂ only

C. O₂ and N₂

D. NH₃

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Correct Answer: Option A

Explanation:
SO₂ from burning coal and NOₓ from vehicles form H₂SO₄ and HNO₃ in rain. CO₂ forms weak carbonic acid (normal rain pH ~5.6). Ammonia is basic and neutralizes acidity.

This question belongs to: Science chemistry

Question #856

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The half-life of a radioactive element is 10 days. After 40 days, the fraction remaining is:

A. 1/2

B. 1/8

C. 1/16

D. 1/4

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Correct Answer: Option C

Explanation:
Number of half-lives = 40/10 = 4. Remaining fraction = (1/2)⁴ = 1/16. So after 4 half-lives, 1/16 of original amount remains.

This question belongs to: Science chemistry

Question #857

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The scientist who proposed the nuclear model of the atom was:

A. J.J. Thomson

B. John Dalton

C. Niels Bohr

D. Ernest Rutherford

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Correct Answer: Option D

Explanation:
Rutherford's gold foil experiment (1911) showed that most of the atom is empty space with a dense positively charged nucleus. Thomson proposed the plum pudding model; Bohr gave quantized orbits; Dalton gave solid sphere model.

This question belongs to: Science chemistry

Question #858

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Mendeleev's periodic table left a gap for an element he called eka-aluminium. This element is now known as:

A. Germanium

B. Silicon

C. Scandium

D. Gallium

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Correct Answer: Option D

Explanation:
Eka-aluminium was later discovered and named gallium. Eka-silicon is germanium; eka-boron is scandium. Mendeleev's predictions were remarkably accurate.

This question belongs to: Science chemistry

Question #859

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The force holding atoms together in a covalent bond is:

A. Electrostatic attraction between ions

B. Gravitational force

C. Magnetic force

D. Attraction between nucleus and shared electrons

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Correct Answer: Option D

Explanation:
In a covalent bond, atoms share pairs of electrons; the shared electrons are attracted to the nuclei of both atoms, holding them together. Ionic bonds involve electrostatic attraction between oppositely charged ions.

This question belongs to: Science chemistry

Question #860

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An element 'X' has electronic configuration 2,8,7. It belongs to:

A. Group 18, Period 3

B. Group 16, Period 3

C. Group 17, Period 3

D. Group 7, Period 2

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Correct Answer: Option C

Explanation:
Atomic number = 2+8+7=17 (chlorine). Period = number of shells = 3. Valence electrons = 7 → Group 17 (10+7 for p-block). Group 18 has 8 valence electrons.

This question belongs to: Science chemistry

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