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 #461
The main difference between diamond and graphite is:
A. Arrangement of carbon atoms
B. Presence of hydrogen
C. Chemical formula
D. Carbon content
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Correct Answer: Option A

Explanation:
Both diamond and graphite are allotropes of carbon, having the same chemical element but different structural arrangements: diamond has a tetrahedral 3D network, graphite has layered planar structure. This leads to differing physical properties (hardness, conductivity).
This question belongs to: Science chemistry
Question #462
The IUPAC name of ethylene is:
A. Ethene
B. Ethane
C. Methane
D. Ethyne
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Correct Answer: Option A

Explanation:
Ethylene (C₂H₄) is systematically named ethene. The -ene suffix indicates a double bond. Ethane is C₂H₆, ethyne (acetylene) is C₂H₂, methane is CH₄. Ethene is an important petrochemical used to make polythene.
This question belongs to: Science chemistry
Question #463
Which of the following is a fossil fuel?
A. Solar energy
B. Biogas
C. Hydrogen
D. Natural gas
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Correct Answer: Option D

Explanation:
Natural gas (mainly methane) is a fossil fuel formed from ancient organic matter. Biogas is a renewable fuel from recent organic waste. Hydrogen is an energy carrier, not a fossil fuel. Solar energy is renewable.
This question belongs to: Science chemistry
Question #464
The unit of calorific value is:
A. m/s
B. Pa
C. J/kg
D. N
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Correct Answer: Option C

Explanation:
Calorific value is the amount of heat energy released per unit mass or volume of a fuel completely burned. Common units: J/kg, kJ/kg, kcal/kg, Btu/lb. It indicates fuel quality. Hydrogen has ~142 MJ/kg.
This question belongs to: Science chemistry
Question #465
In electroplating of copper on an iron spoon, the electrolyte used is:
A. Sulfuric acid
B. Iron sulfate
C. Copper sulfate solution
D. Sodium chloride solution
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Correct Answer: Option C

Explanation:
Acidified copper sulfate (CuSO₄) solution is the electrolyte. The iron spoon is the cathode, and a pure copper plate is the anode. Cu²⁺ ions are reduced at the cathode and deposited on the spoon. Fe from spoon does not go into solution because it is cathode.
This question belongs to: Science chemistry
Question #466
A gas at constant temperature expands from 10 L to 20 L. What happens to its pressure?
A. Remains same
B. Doubles
C. Becomes zero
D. Halves
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Correct Answer: Option D

Explanation:
Boyle's law: P₁V₁ = P₂V₂. So P₂ = P₁(V₁/V₂) = P₁(10/20) = P₁/2. Pressure is halved. If volume doubles, pressure halves, assuming constant temperature and amount. This is an inverse relationship.
This question belongs to: Science chemistry
Question #467
Which gas diffuses fastest under identical conditions?
A. CO₂
B. SO₂
C. CH₄
D. Cl₂
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Correct Answer: Option C

Explanation:
Rate ∝ 1/√M. Molar masses: CO₂=44, SO₂=64, CH₄=16, Cl₂=71. Methane has the smallest molar mass, so it diffuses fastest. Graham's law applies.
This question belongs to: Science chemistry
Question #468
Which of the following is a biological catalyst?
A. Platinum
B. Amylase
C. Vanadium pentoxide
D. Iron
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Correct Answer: Option B

Explanation:
Amylase is an enzyme (biological catalyst) that breaks down starch. Platinum, V₂O₅, and iron are inorganic chemical catalysts. Enzymes are proteins, highly specific, and work under mild conditions.
This question belongs to: Science chemistry
Question #469
The extraction of zinc from zinc blende involves roasting to convert it to:
A. ZnSO₄
B. ZnO
C. ZnCl₂
D. Zn metal directly
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Correct Answer: Option B

Explanation:
Roasting: 2ZnS + 3O₂ → 2ZnO + 2SO₂. The oxide is then reduced with coke at high temperature: ZnO + C → Zn + CO. Alternatively, it can be leached with H₂SO₄ and electrolyzed.
This question belongs to: Science chemistry
Question #470
Hydrochloric acid is present in:
A. Milk
B. Orange juice
C. Gastric juice
D. Vinegar
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Correct Answer: Option C

Explanation:
Gastric juice in the stomach contains hydrochloric acid (HCl) which aids digestion and kills bacteria. Orange juice contains citric acid, vinegar acetic acid, milk lactic acid (from fermentation). The pH of stomach acid is around 1-2.
This question belongs to: Science chemistry
Question #471
The alcohol used in antifreeze is:
A. Glycerol
B. Methanol
C. Ethylene glycol
D. Ethanol
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Correct Answer: Option C

Explanation:
Ethylene glycol (1,2-ethanediol) is the main component of antifreeze, lowering the freezing point of water. Methanol is toxic, ethanol can be used but evaporates, glycerol is viscous. Ethylene glycol is poisonous if ingested. Propylene glycol is a safer alternative.
This question belongs to: Science chemistry
Question #472
Which of the following is a synthetic detergent?
A. Starch
B. Soap
C. Cellulose
D. Sodium lauryl sulfate
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Correct Answer: Option D

Explanation:
Sodium lauryl sulfate (SLS) is a synthetic detergent (surfactant) used in shampoos and toothpaste. Soap is a natural detergent from fats/oils. Starch and cellulose are natural polymers, not detergents. SLS has a sulfate group and works well in hard water.
This question belongs to: Science chemistry
Question #473
Glass is a:
A. Crystalline solid
B. Amorphous solid
C. Molecular solid
D. Ionic solid
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Correct Answer: Option B

Explanation:
Glass is an amorphous (non-crystalline) solid; it lacks a long-range ordered structure. It is sometimes called a supercooled liquid. It softens over a temperature range rather than having a sharp melting point. Quartz (SiO₂) is crystalline.
This question belongs to: Science chemistry
Question #474
Rubber is made more strong and elastic by the process of:
A. Hydrogenation
B. Saponification
C. Vulcanization
D. Fermentation
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Correct Answer: Option C

Explanation:
Vulcanization involves heating natural rubber with sulfur, forming cross-links between polymer chains. This improves elasticity, tensile strength, and resistance to temperature changes. Hydrogenation adds H₂, saponification makes soap, fermentation produces alcohol.
This question belongs to: Science chemistry
Question #475
Water that does not lather easily with soap is called:
A. Soft water
B. Rain water
C. Hard water
D. Distilled water
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Correct Answer: Option C

Explanation:
Hard water contains dissolved Ca²⁺ and Mg²⁺ ions which react with soap to form insoluble scum, preventing lather. Soft water lathers readily. Distilled water is pure (soft). Rainwater is naturally soft but may dissolve CO₂ and become slightly acidic.
This question belongs to: Science chemistry
Question #476
The process of killing microorganisms in water using ultraviolet light is called:
A. Ozonation
B. Chlorination
C. UV irradiation
D. Boiling
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Correct Answer: Option C

Explanation:
UV irradiation uses ultraviolet light to disrupt the DNA of microorganisms, rendering them unable to reproduce and cause disease. It is a physical disinfection method, leaving no chemical residue. Chlorination uses chlorine, ozonation uses ozone, boiling uses heat.
This question belongs to: Science chemistry
Question #477
Which of the following gases is responsible for the greenhouse effect?
A. Argon
B. Nitrogen
C. Oxygen
D. Methane
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Correct Answer: Option D

Explanation:
Methane (CH₄) is a potent greenhouse gas, absorbing infrared radiation. Oxygen and nitrogen are diatomic and do not absorb IR. Argon is a noble gas, inert. Greenhouse gases include CO₂, CH₄, N₂O, CFCs, H₂O vapor.
This question belongs to: Science chemistry
Question #478
Alpha rays consist of:
A. Neutrons
B. Helium nuclei
C. Electrons
D. Protons
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Correct Answer: Option B

Explanation:
Alpha particles are identical to helium-4 nuclei (2 protons + 2 neutrons), with a +2 charge. They are emitted during radioactive decay of heavy elements like uranium. They have low penetration power. Beta rays are electrons, gamma rays are photons.
This question belongs to: Science chemistry
Question #479
The half-life of a radioisotope is the time required for its activity to reduce to:
A. Three-fourths
B. One-fourth
C. Zero
D. One-half of the initial value
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Correct Answer: Option D

Explanation:
Half-life (T₁/₂) is the time taken for the number of radioactive nuclei (or activity) to decrease to half of its original value. It's a constant characteristic of each radioisotope. For example, C-14 half-life is 5730 years.
This question belongs to: Science chemistry
Question #480
Who discovered the nucleus of an atom?
A. Ernest Rutherford
B. James Chadwick
C. J. J. Thomson
D. Niels Bohr
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Correct Answer: Option A

Explanation:
Ernest Rutherford, through the gold foil experiment in 1911, discovered the dense, positively charged nucleus. Thomson discovered the electron, Bohr proposed quantized orbits, Chadwick discovered the neutron. Rutherford also discovered the proton.
This question belongs to: Science chemistry

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