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 #141
The chemical formula of DAP is:
A. (NH₄)₂SO₄
B. (NH₄)₃PO₄
C. NH₄H₂PO₄
D. (NH₄)₂HPO₄
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Correct Answer: Option D

Explanation:
Diammonium phosphate (DAP) is (NH₄)₂HPO₄. It is produced by reacting ammonia with phosphoric acid: 2NH₃ + H₃PO₄ → (NH₄)₂HPO₄. It contains 18% N and 46% P₂O₅. Monoammonium phosphate (MAP) is NH₄H₂PO₄. Ammonium sulfate is (NH₄)₂SO₄. Triammonium phosphate is unstable. DAP is widely used as a starter fertilizer.
This question belongs to: Science chemistry
Question #142
Hydrochloric acid is also known as:
A. Aqua regia
B. Muriatic acid
C. Carbolic acid
D. Oil of vitriol
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Correct Answer: Option B

Explanation:
Hydrochloric acid (HCl) was historically called muriatic acid or spirits of salt, produced from salt (NaCl) and sulfuric acid. Oil of vitriol is H₂SO₄. Aqua regia is a mixture of 3 parts HCl and 1 part HNO₃. Carbolic acid is phenol. HCl is present in gastric juice and used in metal cleaning and chemical synthesis.
This question belongs to: Science chemistry
Question #143
Which compound is used as a chemical sterilant and bleaching agent?
A. Ethanol
B. Acetone
C. Hydrogen peroxide
D. Methanol
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Correct Answer: Option C

Explanation:
Hydrogen peroxide (H₂O₂) is a strong oxidizing agent that kills microorganisms through oxidative damage and bleaches colored substances. It is used as a disinfectant (3% solution), in hair bleaching, and in the paper textile industry. Ethanol is a disinfectant but not a strong bleaching agent. Methanol is toxic, not used for sterilization. Acetone is a solvent.
This question belongs to: Science chemistry
Question #144
The functional isomer of ethanol (C₂H₅OH) is:
A. Dimethyl ether
B. Acetic acid
C. Ethanal
D. Methoxymethane
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Correct Answer: Option A

Explanation:
Ethanol (CH₃CH₂OH) and dimethyl ether (CH₃OCH₃) have the same molecular formula C₂H₆O but different functional groups: alcohol (-OH) vs ether (-O-). This is functional group isomerism. Ethanal is C₂H₄O, acetic acid C₂H₄O₂. Methoxymethane is another name for dimethyl ether. Functional isomers exhibit different chemical properties; ethanol reacts with Na, ether does not.
This question belongs to: Science chemistry
Question #145
Soap is the sodium or potassium salt of:
A. Sulfonic acids
B. Amino acids
C. Short-chain carboxylic acids
D. Long-chain fatty acids
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Correct Answer: Option D

Explanation:
Soap is made by saponification of triglycerides (fats/oils) which are esters of glycerol and long-chain fatty acids (e.g., stearic, palmitic, oleic). The sodium salt gives hard soap, potassium gives soft soap. The long hydrocarbon chain (hydrophobic) and carboxylate head (hydrophilic) provide cleaning action via micelle formation. Synthetic detergents are usually sodium salts of sulfonic acids or sulfate esters.
This question belongs to: Science chemistry
Question #146
Glass is considered a:
A. Ionic solid
B. Crystalline solid
C. Amorphous solid
D. Molecular solid
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Correct Answer: Option C

Explanation:
Glass is an amorphous (non-crystalline) solid, sometimes called a supercooled liquid. It lacks long-range periodic order; atoms are arranged in a disordered network. It softens over a temperature range rather than having a sharp melting point. Common glass is soda-lime-silicate glass. Crystalline solids have sharp melting points and regular lattice structures (e.g., NaCl, quartz).
This question belongs to: Science chemistry
Question #147
Plastics are polymers that can be molded when heated. Which of the following is a thermosetting plastic?
A. Bakelite
B. PVC
C. Polyethylene
D. Nylon
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Correct Answer: Option A

Explanation:
Bakelite is a thermosetting plastic (phenol-formaldehyde resin). Once set, it cannot be remolded by heating because its polymer chains are cross-linked. Polyethylene, PVC, and nylon are thermoplastics—they can be repeatedly softened by heat and hardened on cooling. Thermosetting plastics are used for electrical switches, handles, and adhesives. Vulcanized rubber is also thermoset.
This question belongs to: Science chemistry
Question #148
Natural rubber is a polymer of:
A. Styrene
B. Isoprene
C. Vinyl chloride
D. Ethene
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Correct Answer: Option B

Explanation:
Natural rubber (cis-1,4-polyisoprene) is an addition polymer of isoprene (2-methyl-1,3-butadiene). It is obtained from latex of rubber tree (Hevea brasiliensis). It is elastic but weak. Vulcanization with sulfur introduces cross-links, improving strength and elasticity. Ethene gives polyethylene; styrene gives polystyrene; vinyl chloride gives PVC.
This question belongs to: Science chemistry
Question #149
The purity of water can be checked by measuring its:
A. Boiling point
B. Viscosity
C. Surface tension
D. Specific conductance
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Correct Answer: Option D

Explanation:
Pure water is a poor conductor of electricity. The presence of dissolved ionic impurities (salts) increases conductivity. Measuring specific conductance (or resistivity) is a quick method to check water purity; ultrapure water has conductivity ~0.055 µS/cm. Boiling point elevation also indicates impurities but is less sensitive for trace amounts. Conductivity meters are widely used in laboratories.
This question belongs to: Science chemistry
Question #150
The ozone layer is found in which layer of the atmosphere?
A. Thermosphere
B. Troposphere
C. Stratosphere
D. Mesosphere
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Correct Answer: Option C

Explanation:
The ozone layer is located in the lower stratosphere (~15-35 km altitude), where ozone concentration is highest. It absorbs harmful ultraviolet radiation (UV-B and UV-C) from the sun. Ground-level ozone (troposphere) is a pollutant and component of smog, harmful to health. Ozone depletion is caused by chlorofluorocarbons (CFCs) which release chlorine atoms that catalytically destroy O₃.
This question belongs to: Science chemistry
Question #151
Acid rain can damage buildings made of marble because marble is:
A. Calcium carbonate
B. Magnesium oxide
C. Calcium silicate
D. Aluminium oxide
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Correct Answer: Option A

Explanation:
Marble is primarily calcium carbonate (CaCO₃). It reacts with acid rain (containing H₂SO₄ and HNO₃) to form soluble salts, causing erosion: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. This is why monuments like Taj Mahal are affected. CaCO₃ is basic, so it neutralizes acid. Restoration and pollution control are needed to protect heritage.
This question belongs to: Science chemistry
Question #152
Which radioactive isotope is used in the treatment of cancer?
A. Cobalt-60
B. Uranium-235
C. Iodine-131
D. Carbon-14
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Correct Answer: Option A

Explanation:
Cobalt-60 is a gamma-ray emitter used in radiotherapy to destroy cancerous cells. Iodine-131 is used for thyroid cancer and disorders. Carbon-14 is used in radiocarbon dating. Uranium-235 is used as fuel in nuclear reactors and weapons. Radioisotopes for medical use are produced in nuclear reactors. Gamma rays penetrate and damage DNA of rapidly dividing cells.
This question belongs to: Science chemistry
Question #153
The half-life of a substance is 4 years. In how many years will 1/16 of the original amount remain?
A. 8 years
B. 20 years
C. 12 years
D. 16 years
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Correct Answer: Option D

Explanation:
Fraction remaining = (1/2)^n = 1/16 => n = 4 half-lives. Time = n × half-life = 4 × 4 = 16 years. After 1 half-life: 1/2, 2: 1/4, 3: 1/8, 4: 1/16. Radioactive decay is exponential. So after 16 years, only 1/16th of original radioactive atoms remain.
This question belongs to: Science chemistry
Question #154
Who is credited with the discovery of the atomic nucleus through the gold foil experiment?
A. Ernest Rutherford
B. John Dalton
C. J. J. Thomson
D. James Chadwick
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Correct Answer: Option A

Explanation:
Ernest Rutherford, in 1911, along with Geiger and Marsden, bombarded a thin gold foil with alpha particles. Most passed through, some were deflected at large angles, leading to the nuclear model of the atom—a small, dense, positively charged nucleus with electrons around it. Thomson's plum pudding model predicted no large deflections. Chadwick discovered neutron.
This question belongs to: Science chemistry
Question #155
Which of the following is an example of a pure substance?
A. Air
B. Milk
C. Sea water
D. Distilled water
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Correct Answer: Option D

Explanation:
Distilled water is a pure compound (H₂O) with a fixed composition and distinct properties. Milk is a colloid of fat, protein, etc. Air is a homogeneous mixture of gases. Sea water is a solution of salts. Pure substances are either elements or compounds; mixtures contain two or more substances physically combined. Distillation removes dissolved salts and impurities.
This question belongs to: Science chemistry
Question #156
Which change is exothermic?
A. Evaporation of water
B. Melting of ice
C. Sublimation of camphor
D. Combustion of methane
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Correct Answer: Option D

Explanation:
Combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O + heat) is an exothermic reaction, releasing heat to surroundings. Melting, evaporation, and sublimation are endothermic phase changes requiring heat absorption to overcome intermolecular forces. Exothermic reactions: burning, respiration, neutralization (usually), condensation, freezing. Endothermic: photosynthesis, cooking, melting, boiling.
This question belongs to: Science chemistry
Question #157
Separation of a mixture of naphthalene and sand can be achieved by:
A. Sublimation
B. Filtration
C. Magnetic separation
D. Distillation
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Correct Answer: Option A

Explanation:
Naphthalene sublimes on heating, directly changing to vapor, while sand remains. The naphthalene vapor can be condensed on a cold surface. This technique works for any mixture where one component sublimes (naphthalene, camphor, NH₄Cl). Filtration works for insoluble solids in liquids. Magnetic separation for magnetic ores. Distillation for liquid mixtures.
This question belongs to: Science chemistry
Question #158
Which of the following is a chemical property of a substance?
A. Reactivity with acid
B. Boiling point
C. Melting point
D. Density
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Correct Answer: Option A

Explanation:
Chemical properties describe a substance's ability to undergo chemical changes—reactivity with acid, flammability, oxidation states, etc. Melting point, density, boiling point are physical properties that can be observed without changing composition. Reactivity with acid involves formation of new substances. A piece of magnesium reacting with HCl is a chemical change.
This question belongs to: Science chemistry
Question #159
A molecule is defined as the smallest particle of a substance that can exist independently and retain its:
A. Physical state
B. Volume
C. Chemical properties
D. Mass
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Correct Answer: Option C

Explanation:
A molecule is a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction while retaining the composition and chemical properties of that substance. For example, H₂O molecule shows properties of water. Atoms (like He) can also be independent, but a molecule of an element (O₂) or compound retains identity.
This question belongs to: Science chemistry
Question #160
Isotopes differ in the number of:
A. Electrons
B. Protons
C. Neutrons
D. Positrons
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Correct Answer: Option C

Explanation:
Isotopes are atoms of the same element with the same atomic number (protons) but different mass numbers due to varying number of neutrons. For example, protium (¹H) has 0 neutrons, deuterium (²H) has 1, tritium (³H) has 2. Chemical properties are nearly identical because electronic configuration is the same, but physical properties (mass, density) differ.
This question belongs to: Science chemistry

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