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 #421
In electroplating, the metal to be plated is made the:
A. Anode
B. Electrolyte
C. Cathode
D. Salt bridge
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Correct Answer: Option C

Explanation:
The object to be plated is connected to the negative terminal (cathode). Metal ions from the electrolyte are reduced and deposited on the cathode. The anode is usually the plating metal, which dissolves to replenish the electrolyte. For example, in silver plating, the article is the cathode and silver bar is the anode.
This question belongs to: Science chemistry
Question #422
According to Boyle's law, at constant temperature, the pressure of a gas is inversely proportional to its:
A. Mass
B. Temperature
C. Density
D. Volume
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Correct Answer: Option D

Explanation:
Boyle's law: P ∝ 1/V or PV = constant at constant T and n. So if volume increases, pressure decreases. This is because gas molecules have more space and hit the walls less frequently. An example is a syringe: pulling the plunger increases volume, decreases pressure.
This question belongs to: Science chemistry
Question #423
Graham's law deals with:
A. Rate of diffusion and molar mass
B. Current and time
C. Volume and temperature
D. Pressure and volume
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Correct Answer: Option A

Explanation:
Graham's law of effusion/diffusion: Rate ∝ 1/√M (molar mass) at same temperature and pressure. Lighter gases diffuse faster. This is used in isotope separation (e.g., ²³⁵UF₆ vs ²³⁸UF₆) and in understanding gas behavior in leaks.
This question belongs to: Science chemistry
Question #424
A catalyst increases the rate of a reaction by:
A. Increasing the activation energy
B. Changing the equilibrium constant
C. Providing an alternative path with lower activation energy
D. Increasing the temperature
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Correct Answer: Option C

Explanation:
A catalyst lowers the activation energy barrier by providing a different reaction mechanism. This allows more reactant molecules to have sufficient energy to react. It does not change the thermodynamics (ΔH, equilibrium constant) or get consumed in the reaction. Enzymes are biological catalysts.
This question belongs to: Science chemistry
Question #425
Which enzyme breaks down starch into sugars?
A. Lipase
B. Amylase
C. Trypsin
D. Pepsin
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Correct Answer: Option B

Explanation:
Amylase (present in saliva and pancreatic juice) hydrolyses starch into maltose and dextrins. Pepsin digests proteins in the stomach. Lipase breaks down fats. Trypsin also digests proteins. Enzymes are specific biocatalysts.
This question belongs to: Science chemistry
Question #426
The process of obtaining a metal from its ore by heating with a reducing agent is called:
A. Calcination
B. Roasting
C. Smelting
D. Leaching
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Correct Answer: Option C

Explanation:
Smelting involves heating the concentrated ore (often after roasting/calcination) with a reducing agent (like coke, CO) to reduce the metal oxide to the metal. For example, iron ore is smelted in a blast furnace. Roasting heats sulfide ores in air; calcination heats carbonate ores in absence of air; leaching dissolves out the metal.
This question belongs to: Science chemistry
Question #427
The chief ore of aluminium is:
A. Haematite
B. Zinc blende
C. Bauxite
D. Magnetite
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Correct Answer: Option C

Explanation:
Bauxite (Al₂O₃·2H₂O) is the principal ore of aluminium. Magnetite (Fe₃O₄) and haematite (Fe₂O₃) are iron ores. Zinc blende is ZnS. Bauxite is refined by Bayer's process to obtain pure alumina, which is then electrolyzed in cryolite.
This question belongs to: Science chemistry
Question #428
Urea is manufactured by reacting ammonia with:
A. Hydrochloric acid
B. Sulfuric acid
C. Nitric acid
D. Carbon dioxide
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Correct Answer: Option D

Explanation:
Urea, CO(NH₂)₂, is produced from ammonia and carbon dioxide under high pressure (~200 atm) and temperature (~200°C): 2NH₃ + CO₂ → NH₄COONH₂ (ammonium carbamate) → (NH₂)₂CO + H₂O. It is the most concentrated nitrogenous solid fertilizer.
This question belongs to: Science chemistry
Question #429
NPK fertiliser provides:
A. Nitrogen, Phosphorus, Potassium
B. Nitrogen, Phosphorus, Calcium
C. Nitrogen, Potassium, Calcium
D. Sodium, Phosphorus, Potassium
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Correct Answer: Option A

Explanation:
NPK stands for Nitrogen (N), Phosphorus (P, as P₂O₅), and Potassium (K, as K₂O). These are primary macronutrients essential for plant growth. The numbers on a fertiliser bag (e.g., 10-26-26) indicate the percentage of N, P₂O₅, and K₂O.
This question belongs to: Science chemistry
Question #430
Sulphuric acid is manufactured by:
A. Ostwald process
B. Solvay process
C. Contact process
D. Haber process
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Correct Answer: Option C

Explanation:
The Contact process produces sulphuric acid: S + O₂ → SO₂; 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst); SO₃ + H₂SO₄ → H₂S₂O₇ (oleum); H₂S₂O₇ + H₂O → 2H₂SO₄. Haber process for NH₃, Ostwald for HNO₃, Solvay for Na₂CO₃.
This question belongs to: Science chemistry
Question #431
Which acid is present in the sting of an ant?
A. Acetic acid
B. Lactic acid
C. Methanoic acid
D. Citric acid
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Correct Answer: Option C

Explanation:
Ant sting contains formic acid (methanoic acid, HCOOH). It causes a burning sensation. It can be neutralized by applying a mild base like baking soda. Acetic acid is in vinegar, citric acid in lemons, lactic acid in curd.
This question belongs to: Science chemistry
Question #432
Sodium hydroxide (caustic soda) is manufactured by:
A. Contact process
B. Haber process
C. Chlor-alkali process
D. Ostwald process
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Correct Answer: Option C

Explanation:
The chlor-alkali process electrolyzes concentrated NaCl solution (brine) to produce NaOH, Cl₂, and H₂. 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂. The mercury, diaphragm, or membrane cell can be used. Contact process is for H₂SO₄, Haber for NH₃, Ostwald for HNO₃.
This question belongs to: Science chemistry
Question #433
Hydrogen peroxide is used as a bleaching agent because it:
A. Dehydrates the cloth
B. Is a strong oxidizing agent
C. Absorbs light
D. Is a strong acid
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Correct Answer: Option B

Explanation:
H₂O₂ acts as an oxidizing agent, breaking down colored organic compounds into colorless products. It bleaches hair, textiles, and paper. It also acts as a disinfectant. It decomposes to water and oxygen, leaving no harmful residue, making it environmentally friendly.
This question belongs to: Science chemistry
Question #434
Ethanol is produced by the fermentation of:
A. Protein
B. Fats
C. Starch
D. Glucose
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Correct Answer: Option D

Explanation:
Fermentation of sugars (glucose, fructose) by yeast enzymes produces ethanol and carbon dioxide: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Starch is first hydrolysed to glucose. Proteins and fats are not directly fermented to ethanol.
This question belongs to: Science chemistry
Question #435
Soap is not suitable for washing in hard water because it forms:
A. Soluble sodium salts
B. Foam
C. Insoluble calcium and magnesium salts (scum)
D. Micelles
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Correct Answer: Option C

Explanation:
Soap (sodium carboxylate) reacts with Ca²⁺ and Mg²⁺ ions present in hard water to form an insoluble precipitate known as scum. This reduces lathering and wastage of soap. Synthetic detergents do not form scum because their calcium/magnesium salts are soluble.
This question belongs to: Science chemistry
Question #436
Detergents are better than soaps because they:
A. Are cheaper
B. Have no environmental impact
C. Are natural products
D. Work well in hard water
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Correct Answer: Option D

Explanation:
Synthetic detergents (like alkyl sulfates or sulfonates) form soluble calcium and magnesium salts, so they lather well even in hard water. Soaps form scum. Detergents are usually derived from petrochemicals, can be non-biodegradable if branched, and may cause pollution.
This question belongs to: Science chemistry
Question #437
Cement is a mixture of:
A. Calcium silicates and aluminates
B. Sodium chloride and silica
C. Calcium carbonate only
D. Magnesium oxide and clay
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Correct Answer: Option A

Explanation:
Portland cement is primarily composed of tricalcium silicate (3CaO·SiO₂), dicalcium silicate (2CaO·SiO₂), tricalcium aluminate (3CaO·Al₂O₃), and tetracalcium aluminoferrite. These compounds are formed by heating limestone and clay at high temperatures and then grinding with gypsum.
This question belongs to: Science chemistry
Question #438
Which polymer is used to make non-stick kitchen utensils?
A. Polyethylene
B. Teflon
C. Polystyrene
D. Nylon
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Correct Answer: Option B

Explanation:
Teflon (PTFE) has a very low coefficient of friction and high heat resistance, making it ideal for non-stick coatings. Polystyrene is used in packaging, polyethylene in plastic bags, nylon in textiles and ropes. Teflon's monomer is tetrafluoroethene.
This question belongs to: Science chemistry
Question #439
PVC stands for:
A. Polyvinyl chloride
B. Polyvinyl chlorate
C. Polyvinyl carbon
D. Polyvinyl carbide
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Correct Answer: Option A

Explanation:
PVC (polyvinyl chloride) is a polymer of vinyl chloride (CH₂=CHCl). It is used in pipes, electrical insulation, and flooring. It can be rigid (uPVC) or flexible with plasticizers. It is a thermoplastic. Chlorate/carbon/carbide are not correct expansions.
This question belongs to: Science chemistry
Question #440
Chlorine is added to drinking water to:
A. Improve taste
B. Add minerals
C. Kill harmful microorganisms
D. Remove suspended particles
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Correct Answer: Option C

Explanation:
Chlorination is a disinfection process. Chlorine reacts with water to form hypochlorous acid, which kills bacteria and viruses. It also provides residual protection in distribution pipes. Filtration removes particles; chlorine does not remove dissolved minerals or improve taste significantly; it can cause taste issues if excess.
This question belongs to: Science chemistry

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