chemistry MCQs

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chemistry MCQs

Practice complete Chemistry MCQs covering Matter, States of Matter, Physical and Chemical Changes, Atomic Structure, Chemical Bonding, Periodic Table, Acids, Bases and Salts, Metals and Non-Metals, Chemical Reactions, Electrochemistry, Organic Chemistry, Hydrocarbons, Environmental Chemistry, Polymers, Biomolecules, Nuclear Chemistry, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Question #801
The setting of cement is an:
A. Exothermic process
B. Oxidation process
C. Evaporation process
D. Endothermic process
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Correct Answer: Option A

Explanation:
Hydration of cement is exothermic (heat of hydration). In large concrete pours, this heat can cause thermal cracking. Cooling is sometimes needed.
This question belongs to: Science chemistry
Question #802
Which polymer is used in making bulletproof glass?
A. Bakelite
B. Polycarbonate
C. Polyethylene
D. PVC
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Correct Answer: Option B

Explanation:
Polycarbonate is a tough, transparent thermoplastic used in bulletproof glass, CDs, and lenses. Polyethylene is for bags; PVC for pipes; Bakelite is thermoset.
This question belongs to: Science chemistry
Question #803
Vulcanized rubber has better properties due to:
A. Cross-linking of polymer chains with sulfur
B. Addition of carbon black
C. Addition of plasticizers
D. Removal of impurities
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Correct Answer: Option A

Explanation:
Sulfur forms disulfide cross-links between polyisoprene chains, providing elasticity, tensile strength, and resistance to temperature changes. Carbon black is filler/additive for reinforcement but not the vulcanization agent.
This question belongs to: Science chemistry
Question #804
Which of the following water purification methods can remove dissolved salts?
A. Reverse osmosis
B. Chlorination
C. Ozonation
D. Filtration
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Correct Answer: Option A

Explanation:
Reverse osmosis uses a semipermeable membrane to reject dissolved salts and impurities. Filtration removes solids; chlorination/ozonation disinfect but do not remove salts.
This question belongs to: Science chemistry
Question #805
Acid rain corrodes marble (CaCO₃) because:
A. Acid causes dehydration of marble
B. Marble oxidizes
C. Acid reacts with CaCO₃ forming soluble salts and CO₂
D. Marble is soluble in water
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Correct Answer: Option C

Explanation:
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. Marble monuments like Taj Mahal are damaged. CaSO₄ is slightly soluble and can be washed away.
This question belongs to: Science chemistry
Question #806
Which of the following is a greenhouse gas emitted from paddy fields?
A. Argon
B. Nitrogen
C. Oxygen
D. Methane
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Correct Answer: Option D

Explanation:
Flooded rice paddies promote anaerobic decomposition of organic matter, producing methane (CH₄). It is a potent greenhouse gas. Livestock also emit methane.
This question belongs to: Science chemistry
Question #807
Which radioactive emission has the highest ionizing power?
A. Alpha
B. Beta
C. Gamma
D. X-rays
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Correct Answer: Option A

Explanation:
Alpha particles, being heavy and doubly charged, cause intense ionization over a short distance. They are least penetrating. Gamma has low ionization but high penetration.
This question belongs to: Science chemistry
Question #808
A radioactive sample decays to 1/4 of its original amount in 40 days. Its half-life is:
A. 10 days
B. 20 days
C. 80 days
D. 40 days
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Correct Answer: Option B

Explanation:
1/4 = (1/2)², so 2 half-lives = 40 days → half-life = 20 days. After 1 half-life 1/2 remains, after 2 half-lives 1/4.
This question belongs to: Science chemistry
Question #809
The scientist who discovered radioactivity was:
A. Curie
B. Rutherford
C. Becquerel
D. Chadwick
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Correct Answer: Option C

Explanation:
Henri Becquerel discovered radioactivity in 1896 while studying uranium salts. Marie and Pierre Curie further investigated radioactive elements. Rutherford studied alpha/beta radiation.
This question belongs to: Science chemistry
Question #810
Which of the following changes is an example of a chemical change?
A. Dissolving sugar in water
B. Melting of ice
C. Burning of magnesium ribbon
D. Boiling of water
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Correct Answer: Option C

Explanation:
Burning of magnesium ribbon produces a new substance, magnesium oxide (MgO), and releases heat and light, which are indicators of a chemical change. Melting, dissolving, and boiling are physical changes because the chemical composition remains unchanged. Chemical changes are generally irreversible.
This question belongs to: Science chemistry
Question #811
The separation technique used to obtain different fractions from petroleum is:
A. Simple distillation
B. Sublimation
C. Filtration
D. Fractional distillation
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Correct Answer: Option D

Explanation:
Petroleum is a mixture of hydrocarbons with close boiling points. Fractional distillation uses a fractionating column to separate them efficiently based on repeated condensation–vaporization cycles. Simple distillation cannot separate liquids with boiling point difference less than 25 K effectively. Filtration and sublimation are not applicable.
This question belongs to: Science chemistry
Question #812
Which of the following is an extensive property?
A. Temperature
B. Refractive index
C. Density
D. Enthalpy
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Correct Answer: Option D

Explanation:
Extensive properties depend on the amount of substance. Enthalpy (heat content) is extensive because it scales with the quantity. Temperature, density, and refractive index are intensive properties; they remain constant regardless of the sample size. For example, 1 kg of water has more enthalpy than 1 g of water at the same temperature.
This question belongs to: Science chemistry
Question #813
The process of converting a solid directly into vapor without passing through the liquid state is called:
A. Distillation
B. Sublimation
C. Condensation
D. Evaporation
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Correct Answer: Option B

Explanation:
Sublimation is the direct transition from solid to gas phase. Examples: naphthalene, camphor, iodine, solid CO₂ (dry ice). Evaporation is liquid to gas; condensation is gas to liquid; distillation separates liquid mixtures based on boiling points.
This question belongs to: Science chemistry
Question #814
Two isotopes of an element have the same:
A. Atomic number
B. Number of neutrons
C. Mass number
D. Physical properties
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Correct Answer: Option A

Explanation:
Isotopes have identical atomic numbers (number of protons) but different mass numbers due to different numbers of neutrons. They have similar chemical properties but different physical properties like mass and density. Example: ¹²C and ¹⁴C, both have 6 protons.
This question belongs to: Science chemistry
Question #815
An atom has mass number 39 and 20 neutrons. Its atomic number is:
A. 20
B. 19
C. 39
D. 59
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Correct Answer: Option B

Explanation:
Atomic number (Z) = Mass number (A) – Number of neutrons (N) = 39 – 20 = 19. This is potassium (K). Number of protons equals atomic number. In a neutral atom, electrons also equal Z.
This question belongs to: Science chemistry
Question #816
Which type of bond is formed by the transfer of electrons from a metal to a non-metal?
A. Ionic bond
B. Covalent bond
C. Hydrogen bond
D. Coordinate bond
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Correct Answer: Option A

Explanation:
Ionic (electrovalent) bond involves complete transfer of one or more valence electrons. Example: Na → Na⁺ + e⁻, Cl + e⁻ → Cl⁻, forming NaCl. Covalent bond shares electrons; coordinate bond is a special covalent bond where one atom donates both electrons.
This question belongs to: Science chemistry
Question #817
The compound containing a coordinate covalent bond is:
A. NH₄⁺
B. NaCl
C. CH₄
D. H₂O
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Correct Answer: Option A

Explanation:
Ammonium ion (NH₄⁺) is formed when NH₃ donates its lone pair to H⁺, forming a coordinate (dative) bond. CH₄ and H₂O have ordinary covalent bonds; NaCl is ionic. In NH₄⁺, all four N–H bonds become equivalent.
This question belongs to: Science chemistry
Question #818
The modern periodic table arranges elements in order of increasing:
A. Atomic mass
B. Number of neutrons
C. Atomic number
D. Mass number
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Correct Answer: Option C

Explanation:
The modern periodic law, established by Henry Moseley, states that the properties of elements are periodic functions of their atomic numbers. Mendeleev’s original table was based on atomic mass, but the modern version uses atomic number which resolves anomalies like Ar (Z=18, mass 40) and K (Z=19, mass 39).
This question belongs to: Science chemistry
Question #819
Across a period from left to right, atomic radius generally:
A. Decreases
B. Remains constant
C. Increases
D. First increases then decreases
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Correct Answer: Option A

Explanation:
Atomic radius decreases across a period because the effective nuclear charge increases while electrons are added to the same shell, pulling the electron cloud closer. Down a group, radius increases due to addition of new shells.
This question belongs to: Science chemistry
Question #820
The reaction 2H₂O → 2H₂ + O₂ is a:
A. Double displacement reaction
B. Decomposition reaction
C. Combination reaction
D. Displacement reaction
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Correct Answer: Option B

Explanation:
Water breaks down into hydrogen and oxygen when electricity is passed (electrolysis). A single reactant yields two or more products, hence decomposition. It is also a redox reaction. Combination is the opposite; displacement involves replacing an ion.
This question belongs to: Science chemistry

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