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 #681
James Chadwick discovered the neutron in the year:
A. 1897
B. 1911
C. 1932
D. 1913
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Correct Answer: Option C

Explanation:
James Chadwick discovered the neutron in 1932. He bombarded beryllium with alpha particles and observed a highly penetrating, neutral radiation, which he identified as neutrons. This discovery explained isotopes and completed the basic picture of the atom's subatomic particles.
This question belongs to: Science chemistry
Question #682
Who is credited with the discovery of the nucleus through the alpha-particle scattering experiment?
A. Ernest Rutherford
B. J.J. Thomson
C. James Chadwick
D. Niels Bohr
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Correct Answer: Option A

Explanation:
Ernest Rutherford, along with his students Geiger and Marsden, conducted the famous gold foil experiment in 1911. By observing that a few alpha particles bounced back, he concluded that the atom has a small, dense, positively charged center called the nucleus.
This question belongs to: Science chemistry
Question #683
The oil drop experiment to determine the charge of an electron was performed by:
A. Robert Millikan
B. James Chadwick
C. Ernest Rutherford
D. J.J. Thomson
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Correct Answer: Option A

Explanation:
Robert Millikan performed the oil drop experiment in 1909. By observing charged oil droplets in an electric field, he accurately determined the elementary charge of an electron (e = 1.6 × 10⁻¹⁹ C). This, combined with Thomson's e/m ratio, allowed calculating the electron's mass.
This question belongs to: Science chemistry
Question #684
Which scientist proposed the 'Plum Pudding' model of the atom?
A. John Dalton
B. Ernest Rutherford
C. J.J. Thomson
D. Niels Bohr
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Correct Answer: Option C

Explanation:
J.J. Thomson proposed the 'Plum Pudding' model in 1904 after discovering the electron. He envisioned the atom as a sphere of positive charge with negatively charged electrons embedded within it, like plums in a pudding. This was later disproved by Rutherford's gold foil experiment.
This question belongs to: Science chemistry
Question #685
Which of the following is a chemical property of matter?
A. Density
B. Boiling point
C. Melting point
D. Flammability
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Correct Answer: Option D

Explanation:
Flammability describes how a substance reacts with oxygen to burn, which is a chemical change. Boiling point, density, and melting point are physical properties because they can be observed without changing the chemical identity of the substance. Chemical properties are only observed during a chemical reaction.
This question belongs to: Science chemistry
Question #686
The separation technique that uses a porous barrier to separate solids from liquids is:
A. Distillation
B. Filtration
C. Chromatography
D. Sublimation
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Correct Answer: Option B

Explanation:
Filtration uses filter paper or other porous medium that allows liquid to pass but retains solid particles. Distillation separates liquids by boiling points; sublimation separates sublimable solids; chromatography separates based on differential adsorption. Example: separating sand from water.
This question belongs to: Science chemistry
Question #687
Which of the following statements about physical changes is correct?
A. They are always exothermic.
B. Chemical composition remains the same.
C. They are always irreversible.
D. New substances are formed.
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Correct Answer: Option B

Explanation:
Physical changes affect form or state but not chemical composition. They can be reversible (melting/freezing). No new substances form. They may be endothermic or exothermic. Example: dissolving salt in water – salt is still NaCl.
This question belongs to: Science chemistry
Question #688
The process of separating two immiscible liquids uses:
A. Centrifuge
B. Condenser
C. Fractionating column
D. Separating funnel
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Correct Answer: Option D

Explanation:
A separating funnel allows immiscible liquids to form layers; the denser liquid is drained from the bottom. Fractionating column is for miscible liquids with close boiling points, condenser for distillation, centrifuge for separating fine solids or liquids of different densities by spinning.
This question belongs to: Science chemistry
Question #689
An atom has 18 electrons and 22 neutrons. Its mass number is:
A. 18
B. 22
C. 4
D. 40
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Correct Answer: Option D

Explanation:
In a neutral atom, number of protons = number of electrons = 18. Mass number = protons (18) + neutrons (22) = 40. This is ⁴⁰Ar. Number of neutrons alone doesn't determine mass number.
This question belongs to: Science chemistry
Question #690
Isotopes of chlorine are ³⁵Cl and ³⁷Cl. Their atomic numbers are:
A. 17 and 20
B. 17 and 17
C. 35 and 17
D. 35 and 37
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Correct Answer: Option B

Explanation:
Atomic number is the number of protons, which is 17 for all chlorine atoms. Mass numbers differ due to different neutrons (18 and 20). Isotopes have same atomic number, different mass number.
This question belongs to: Science chemistry
Question #691
The valency of aluminium in Al₂O₃ is:
A. 1
B. 3
C. 4
D. 2
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Correct Answer: Option B

Explanation:
Aluminium oxide: Al³⁺ and O²⁻. To balance charges, 2 Al³⁺ (total +6) combine with 3 O²⁻ (total -6). Thus valency of Al is 3. It loses three electrons. Formula determined by criss-cross method.
This question belongs to: Science chemistry
Question #692
The formation of ammonium ion (NH₄⁺) from NH₃ and H⁺ involves:
A. Ionic bond
B. Metallic bond
C. Covalent bond
D. Coordinate bond
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Correct Answer: Option D

Explanation:
NH₃ has a lone pair on nitrogen; it donates this pair to H⁺ to form a coordinate (dative) bond, where both electrons in the bond come from nitrogen. The resulting NH₄⁺ has four equivalent N-H bonds.
This question belongs to: Science chemistry
Question #693
Which of the following compounds has both ionic and covalent bonds?
A. NaOH
B. CH₄
C. NaCl
D. HCl
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Correct Answer: Option A

Explanation:
Sodium hydroxide (NaOH) has ionic bond between Na⁺ and OH⁻, and covalent bond between O and H within OH⁻. NaCl is purely ionic; CH₄ and HCl are purely covalent (polar covalent in HCl, but not ionic).
This question belongs to: Science chemistry
Question #694
Which of the following elements belongs to Group 2, Period 3?
A. Mg
B. Be
C. Ca
D. Sr
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Correct Answer: Option A

Explanation:
Magnesium (Z=12): configuration 2,8,2. Period = number of shells = 3; Group = 2 (2 valence electrons). Be is Group 2, Period 2; Ca is Group 2, Period 4; Sr Period 5.
This question belongs to: Science chemistry
Question #695
Mendeleev predicted the existence of an element 'eka-silicon', later discovered and named:
A. Germanium
B. Scandium
C. Arsenic
D. Gallium
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Correct Answer: Option A

Explanation:
Mendeleev left gaps and predicted properties of eka-boron (scandium), eka-aluminium (gallium), and eka-silicon (germanium). Germanium was discovered in 1886, its properties matched predictions, confirming the periodic law.
This question belongs to: Science chemistry
Question #696
The atomic radius of sodium is larger than that of chlorine because:
A. Sodium is a metal
B. Sodium has fewer electrons
C. Chlorine is a gas
D. Chlorine has greater nuclear charge attracting electrons more strongly
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Correct Answer: Option D

Explanation:
Across period 3, nuclear charge increases (Na: 11+, Cl: 17+) while electrons are added to the same shell. The increased attraction pulls electrons closer, decreasing radius. Na has larger radius despite having fewer electrons.
This question belongs to: Science chemistry
Question #697
Which of the following reactions is a combination reaction?
A. NaCl + AgNO₃ → AgCl + NaNO₃
B. Zn + CuSO₄ → ZnSO₄ + Cu
C. 2Mg + O₂ → 2MgO
D. CaCO₃ → CaO + CO₂
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Correct Answer: Option C

Explanation:
Combination: two or more reactants combine to one product. Mg and O₂ combine to form MgO. A is decomposition; B is displacement; D is double displacement.
This question belongs to: Science chemistry
Question #698
The reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is an example of:
A. Double displacement
B. Displacement
C. Decomposition
D. Combination
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Correct Answer: Option B

Explanation:
Aluminium displaces iron from iron(III) oxide because Al is more reactive. This is a single displacement (or thermite) reaction. Also redox: Al oxidized, Fe reduced. Combination: one product; decomposition: one reactant.
This question belongs to: Science chemistry
Question #699
Oxidation involves:
A. Gain of electrons
B. Loss of electrons
C. Decrease in oxidation number
D. Gain of hydrogen
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Correct Answer: Option B

Explanation:
Oxidation is loss of electrons, increase in oxidation number, or gain of oxygen/loss of hydrogen. Reduction is gain of electrons. Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain).
This question belongs to: Science chemistry
Question #700
In the reaction 2FeCl₃ + H₂S → 2FeCl₂ + 2HCl + S, the reducing agent is:
A. FeCl₃
B. H₂S
C. FeCl₂
D. HCl
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Correct Answer: Option B

Explanation:
H₂S is oxidized (S²⁻ → S, loss of electrons), so it acts as the reducing agent. FeCl₃ is reduced (Fe³⁺ → Fe²⁺) and acts as oxidizing agent. The substance oxidized is the reducing agent.
This question belongs to: Science chemistry

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