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 #381
Which of the following fertilizers is richest in nitrogen content?
A. Ammonium sulfate
B. Sodium nitrate
C. Calcium ammonium nitrate
D. Urea
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Correct Answer: Option D

Explanation:
Urea has about 46% N, highest among solid fertilizers. Ammonium sulfate 21%, sodium nitrate 16%, CAN about 25%. Urea is the most widely used nitrogen fertilizer.
This question belongs to: Science chemistry
Question #382
The acid present in vinegar is:
A. Formic acid
B. Citric acid
C. Acetic acid
D. Lactic acid
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Correct Answer: Option C

Explanation:
Vinegar is a 4-8% solution of acetic acid (CH₃COOH) in water. Formic acid is in ant sting, citric in citrus fruits, lactic in curd. Acetic acid is used as preservative and condiment.
This question belongs to: Science chemistry
Question #383
Sodium chloride (table salt) is obtained from seawater by:
A. Distillation
B. Evaporation
C. Filtration
D. Sublimation
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Correct Answer: Option B

Explanation:
Salt is obtained by evaporation of seawater in shallow ponds. Water evaporates leaving salt behind. Filtration cannot separate dissolved salt. Distillation would give pure water, not salt. Sublimation for sublimable solids.
This question belongs to: Science chemistry
Question #384
The chemical formula of Teflon is:
A. (CH₂-CHCl)ₙ
B. (CF₂-CF₂)ₙ
C. (CH₂-CH₂)ₙ
D. (CH₂-C₆H₅)ₙ
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Correct Answer: Option B

Explanation:
Teflon (PTFE) is polymerized tetrafluoroethene, repeating unit –CF₂–CF₂–. Option A is PVC, C is polythene, D is polystyrene. Teflon is highly inert, used in non-stick cookware.
This question belongs to: Science chemistry
Question #385
Hard water can be softened by adding washing soda because it:
A. Increases pH
B. Removes chlorine
C. Precipitates calcium and magnesium ions as carbonates
D. Kills bacteria
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Correct Answer: Option C

Explanation:
Na₂CO₃ reacts with Ca²⁺/Mg²⁺ to form insoluble CaCO₃/MgCO₃, which are removed. This is permanent hardness removal. Boiling works for temporary hardness. Ion exchange is another method.
This question belongs to: Science chemistry
Question #386
Which of the following causes ozone depletion?
A. SO₂
B. CO₂
C. N₂
D. CFCs
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Correct Answer: Option D

Explanation:
Chlorofluorocarbons (CFCs) release chlorine atoms in stratosphere which catalytically destroy ozone. CO₂ causes global warming, SO₂ acid rain, N₂ is inert. Ozone hole over Antarctica is due to CFCs.
This question belongs to: Science chemistry
Question #387
Radioactive isotope used in dating ancient objects is:
A. Carbon-14
B. Uranium-235
C. Iodine-131
D. Cobalt-60
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Correct Answer: Option A

Explanation:
Carbon-14 dating is used to determine age of organic materials up to ~50,000 years based on its half-life of 5730 years. Cobalt-60 for cancer therapy, iodine-131 for thyroid, uranium-235 for nuclear fuel.
This question belongs to: Science chemistry
Question #388
Which of the following statements about matter is correct?
A. Matter is always visible to the naked eye.
B. All matter is composed of particles.
C. Gases do not have mass.
D. Matter cannot change its state.
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Correct Answer: Option B

Explanation:
All matter is composed of tiny particles (atoms, molecules, or ions). This is a fundamental concept. Matter may not always be visible (e.g., air). It can change states (solid, liquid, gas). Gases have mass; for example, a filled gas cylinder weighs more than an empty one. The particulate nature of matter explains diffusion, Brownian motion, etc.
This question belongs to: Science chemistry
Question #389
The separation technique based on the difference in boiling points of liquids is:
A. Filtration
B. Distillation
C. Sublimation
D. Chromatography
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Correct Answer: Option B

Explanation:
Distillation separates a mixture of two or more miscible liquids with different boiling points. The liquid with the lower boiling point vaporizes first, is condensed, and collected separately. Fractional distillation is used when the boiling point difference is less than 25 K. Simple distillation works for larger differences. Filtration separates solids from liquids; sublimation separates sublimable solids; chromatography separates dissolved substances based on differential adsorption.
This question belongs to: Science chemistry
Question #390
Which of the following is a chemical change?
A. Breaking a glass tumbler
B. Dissolving sugar in water
C. Cooking of food
D. Melting of candle wax
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Correct Answer: Option C

Explanation:
Cooking of food involves chemical reactions (e.g., denaturation of proteins, caramelization of sugars) that form new substances, making it a chemical change. Dissolving sugar in water is a physical change because no new substance is formed (sugar can be recovered by evaporation). Breaking glass is a physical change (change in size/shape). Melting wax is a physical change (change of state).
This question belongs to: Science chemistry
Question #391
Which of the following is an extensive property of matter?
A. Boiling point
B. Density
C. Refractive index
D. Number of moles
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Correct Answer: Option D

Explanation:
Extensive properties depend on the amount of substance. Number of moles (or mass, volume) is extensive. Density, refractive index, boiling point are intensive properties – they do not depend on the quantity. For example, 1 liter of water boils at 100°C, same as 10 liters. Intensive properties are useful for identifying substances.
This question belongs to: Science chemistry
Question #392
A mixture of two immiscible liquids can be separated by:
A. Fractional distillation
B. Separating funnel
C. Centrifugation
D. Simple distillation
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Correct Answer: Option B

Explanation:
Immiscible liquids (e.g., oil and water) form separate layers. A separating funnel is used to draw off the denser liquid from the bottom. Distillation methods are used for miscible liquids. Centrifugation separates solids from liquids or liquids of different densities in a mixture but not for two immiscible liquids efficiently in a lab; a separating funnel is simpler.
This question belongs to: Science chemistry
Question #393
The atomic number of an element is 11. Its electronic configuration is:
A. 2, 8, 8
B. 2, 8, 7
C. 2, 8, 1
D. 2, 8, 2
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Correct Answer: Option C

Explanation:
Atomic number 11 is sodium (Na). The electron shells fill as 2 in K, 8 in L, and the remaining 1 in M. Thus configuration is 2,8,1. It belongs to Group 1 (alkali metals) and Period 3. The configuration determines its valency (1) and reactivity.
This question belongs to: Science chemistry
Question #394
Isotopes of an element have:
A. Same number of neutrons
B. Same atomic number, different mass number
C. Same mass number, different atomic number
D. Same physical properties
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Correct Answer: Option B

Explanation:
Isotopes are atoms of the same element (same atomic number, same number of protons) but different mass numbers due to varying number of neutrons. For example, ¹²C, ¹³C, ¹⁴C. Their chemical properties are similar but physical properties (mass, density, rate of diffusion) differ. Isobars have same mass number but different atomic numbers.
This question belongs to: Science chemistry
Question #395
The valency of oxygen in H₂O is:
A. 4
B. 6
C. 2
D. 1
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Correct Answer: Option C

Explanation:
Oxygen (atomic number 8) has electronic configuration 2,6. It needs 2 more electrons to complete its octet. In water (H₂O), it shares two electrons (one each with two hydrogen atoms), forming two covalent bonds. Hence valency = 2. Oxidation number is -2.
This question belongs to: Science chemistry
Question #396
The formation of MgO from Mg and O₂ involves:
A. No electron transfer
B. Transfer of electrons from O to Mg
C. Sharing of electrons
D. Transfer of electrons from Mg to O
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Correct Answer: Option D

Explanation:
Magnesium oxide (MgO) is an ionic compound. Magnesium (2,8,2) loses two electrons to become Mg²⁺, and oxygen (2,6) gains two electrons to become O²⁻. This electron transfer forms an electrovalent (ionic) bond. Covalent bonds involve sharing (e.g., H₂O).
This question belongs to: Science chemistry
Question #397
The bond in H₂ molecule is:
A. Coordinate bond
B. Non-polar covalent bond
C. Ionic bond
D. Polar covalent bond
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Correct Answer: Option B

Explanation:
In H₂, two hydrogen atoms share their electrons equally because they have the same electronegativity. Thus, a non-polar covalent bond is formed. Ionic bonds form between metals and non-metals. Polar covalent bonds involve unequal sharing (e.g., HCl). Coordinate bonds involve one atom donating both electrons (e.g., NH₄⁺).
This question belongs to: Science chemistry
Question #398
Which of the following contains a coordinate bond?
A. NH₃
B. NaCl
C. H₂O
D. O₃
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Correct Answer: Option D

Explanation:
Ozone (O₃) has a coordinate bond (dative bond). One oxygen atom donates a lone pair to another oxygen atom. The Lewis structure shows O=O⁺–O⁻ or resonance. NaCl is ionic; H₂O has polar covalent bonds; NH₃ has ordinary covalent bonds (though it can donate a lone pair to form coordinate bond in NH₄⁺).
This question belongs to: Science chemistry
Question #399
The modern periodic table is based on:
A. Mass number
B. Atomic mass
C. Atomic number
D. Number of neutrons
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Correct Answer: Option C

Explanation:
The modern periodic law states that properties of elements are periodic functions of their atomic numbers (number of protons). This was established by Henry Moseley. Mendeleev's original table used atomic mass, but the modern table resolves anomalies by ordering by atomic number.
This question belongs to: Science chemistry
Question #400
An element with atomic number 15 belongs to which group and period?
A. Group 15, Period 4
B. Group 3, Period 15
C. Group 15, Period 3
D. Group 5, Period 3
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Correct Answer: Option C

Explanation:
Atomic number 15 is phosphorus. Electronic configuration: 2, 8, 5. Number of shells = 3 (Period 3). Valence electrons = 5, so it is in group 15 (10+5) for p-block elements. Group 5 is for d-block. Thus Group 15, Period 3.
This question belongs to: Science chemistry

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