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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Page 47 of 55
Question #921
The salt formed from strong acid and weak base is:
A. CH₃COONa
B. K₂SO₄
C. NaCl
D. NH₄Cl
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Correct Answer: Option D

Explanation:
NH₄Cl is from HCl (strong) and NH₄OH (weak). Its aqueous solution is acidic due to hydrolysis of NH₄⁺. NaCl is neutral (strong-strong). CH₃COONa basic (weak-strong).
This question belongs to: Science chemistry
Question #922
Bleaching powder is obtained by treating slaked lime with:
A. O₂
B. Cl₂
C. SO₂
D. HCl
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Correct Answer: Option B

Explanation:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. Chlorine gas is passed over dry slaked lime. It is a mixed salt.
This question belongs to: Science chemistry
Question #923
Which of the following metals is the best conductor of heat?
A. Copper
B. Silver
C. Iron
D. Aluminium
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Correct Answer: Option B

Explanation:
Silver has the highest thermal conductivity, followed by copper. It's also the best electrical conductor. Copper is more commonly used due to cost.
This question belongs to: Science chemistry
Question #924
The hardest natural substance is:
A. Graphite
B. Fullerene
C. Diamond
D. Quartz
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Correct Answer: Option C

Explanation:
Diamond, with its tetrahedral covalent network, is the hardest known natural material (Mohs 10). Graphite is soft; quartz is SiO₂, hardness 7.
This question belongs to: Science chemistry
Question #925
Methane on chlorination in sunlight gives:
A. Methyl chloride and HCl
B. Acetylene
C. Carbon tetrachloride only
D. Ethane
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Correct Answer: Option A

Explanation:
CH₄ + Cl₂ → CH₃Cl + HCl (substitution). Further substitution yields CH₂Cl₂, CHCl₃, CCl₄. Sunlight provides free radicals.
This question belongs to: Science chemistry
Question #926
Petroleum is formed from:
A. Decaying land plants only
B. Volcanic ash
C. Meteors
D. Marine organisms buried under sediment
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Correct Answer: Option D

Explanation:
Petroleum originates from microscopic marine organisms (plankton) that sank to the seabed and were transformed by heat/pressure over millions of years. Coal is from land plants.
This question belongs to: Science chemistry
Question #927
The calorific value is highest for:
A. LPG
B. CNG
C. Hydrogen
D. Diesel
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Correct Answer: Option C

Explanation:
Hydrogen has ~150 kJ/g; LPG ~50 kJ/g; CNG ~55 kJ/g; diesel ~45 kJ/g. Hydrogen has highest energy per mass but low density, posing storage challenges.
This question belongs to: Science chemistry
Question #928
In electroplating, the metal to be deposited is taken as:
A. Salt bridge
B. Electrolyte
C. Cathode
D. Anode
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Correct Answer: Option D

Explanation:
The plating metal (e.g., silver) is the anode which dissolves to supply metal ions. The article to be plated is the cathode. Metal ions reduce on cathode.
This question belongs to: Science chemistry
Question #929
Faraday's second law: When same charge is passed, masses deposited are proportional to:
A. Molecular masses
B. Equivalent weights
C. Densities
D. Atomic masses
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Correct Answer: Option B

Explanation:
m₁/m₂ = E₁/E₂ where E = atomic mass / valency. This is Faraday's second law of electrolysis. It relates mass to chemical equivalent.
This question belongs to: Science chemistry
Question #930
If temperature of a gas is kept constant and pressure is doubled, volume becomes:
A. Four times
B. Double
C. Half
D. Same
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Correct Answer: Option C

Explanation:
Boyle's law: P₁V₁ = P₂V₂. If P₂ = 2P₁, then V₂ = V₁/2. Volume is inversely proportional to pressure.
This question belongs to: Science chemistry
Question #931
Which gas diffuses slowest?
A. NH₃
B. H₂
C. CH₄
D. CO₂
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Correct Answer: Option D

Explanation:
Rate ∝ 1/√M. Molar masses: H₂=2, CH₄=16, NH₃=17, CO₂=44. CO₂ has highest mass, diffuses slowest.
This question belongs to: Science chemistry
Question #932
Positive catalysts work by:
A. Consuming reactants
B. Changing equilibrium
C. Increasing activation energy
D. Decreasing activation energy
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Correct Answer: Option D

Explanation:
Catalysts lower activation energy, providing an easier pathway, thus increasing reaction rate. They do not affect equilibrium constant or get consumed.
This question belongs to: Science chemistry
Question #933
Pepsin is an enzyme that digests:
A. Fats
B. Cellulose
C. Proteins
D. Starch
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Correct Answer: Option C

Explanation:
Pepsin, secreted in the stomach, breaks down proteins into peptides. It works in acidic pH. Amylase digests starch; lipase digests fats.
This question belongs to: Science chemistry
Question #934
The process of roasting is used for:
A. Carbonate ores
B. Oxide ores
C. Native metals
D. Sulfide ores
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Correct Answer: Option D

Explanation:
Roasting converts sulfide ores to oxides by heating in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂. Calcination is for carbonates; leaching for others.
This question belongs to: Science chemistry
Question #935
Aqua fortis is the historical name for:
A. Hydrochloric acid
B. Nitric acid
C. Phosphoric acid
D. Sulphuric acid
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Correct Answer: Option B

Explanation:
Nitric acid (HNO₃) was called aqua fortis (strong water) due to its ability to dissolve metals like silver (except gold). Oil of vitriol is H₂SO₄; muriatic acid is HCl.
This question belongs to: Science chemistry
Question #936
The common name of sodium hydroxide is:
A. Caustic soda
B. Baking soda
C. Washing soda
D. Soda ash
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Correct Answer: Option A

Explanation:
NaOH is caustic soda. Washing soda is Na₂CO₃·10H₂O; baking soda NaHCO₃; soda ash anhydrous Na₂CO₃.
This question belongs to: Science chemistry
Question #937
Hydrogen peroxide decomposes to water and oxygen. This reaction is:
A. 2H₂O₂ → 2H₂ + 2O₂
B. H₂O₂ + H₂ → 2H₂O
C. 2H₂O₂ → 2H₂O + O₂
D. H₂O₂ + O → H₂O + O₂
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Correct Answer: Option C

Explanation:
Decomposition of H₂O₂ yields water and O₂. It is catalyzed by MnO₂, light, or enzyme catalase. It's a disproportionation reaction.
This question belongs to: Science chemistry
Question #938
The alcohol that is poisonous and can cause blindness is:
A. Methanol
B. Ethanol
C. Butanol
D. Isopropyl alcohol
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Correct Answer: Option A

Explanation:
Methanol (CH₃OH) is metabolized to formaldehyde and formic acid, causing optic nerve damage, blindness, or death. Ethanol is used in beverages.
This question belongs to: Science chemistry
Question #939
Which of the following is not a synthetic fiber?
A. Acrylic
B. Polyester
C. Silk
D. Nylon
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Correct Answer: Option C

Explanation:
Silk is a natural protein fiber obtained from silkworm cocoons. Nylon, polyester, acrylic are synthetic polymers derived from petrochemicals.
This question belongs to: Science chemistry
Question #940
Cement is mixed with water, it sets into a hard mass due to:
A. Hydration
B. Reduction
C. Evaporation
D. Oxidation
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Correct Answer: Option A

Explanation:
Cement compounds react with water (hydration) forming hydrated silicates and aluminates, which crystallize and interlock, giving strength. This is exothermic.
This question belongs to: Science chemistry

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