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 14 of 55
Question #261
The electrolyte used in copper refining is:
A. AgNO₃
B. NaCl
C. KOH
D. CuSO₄ + H₂SO₄
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Correct Answer: Option D

Explanation:
In electrolytic refining of copper, the electrolyte is acidified copper sulfate solution (CuSO₄ acidified with H₂SO₄). The anode is impure copper, cathode is pure copper. Cu²⁺ ions from the electrolyte are reduced and deposited on the cathode, while copper from anode oxidizes and enters solution. Impurities settle as anode mud (containing Ag, Au).
This question belongs to: Science chemistry
Question #262
Faraday's constant represents:
A. Mass of one electron
B. Charge on one electron
C. Avogadro's number
D. Charge on one mole of electrons
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Correct Answer: Option D

Explanation:
Faraday constant (F) = 96485 C/mol, approximately 96500 C/mol. It is the magnitude of electric charge per mole of electrons. Charge on one electron = 1.602 × 10⁻¹⁹ C, multiplied by Avogadro's number gives F. Used in electrolysis calculations: mass deposited = (Q × M)/(n × F).
This question belongs to: Science chemistry
Question #263
According to Charles' law, at constant pressure, the volume of a gas is directly proportional to its:
A. Absolute temperature
B. Density
C. Temperature in Celsius
D. Pressure
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Correct Answer: Option A

Explanation:
Charles' law: V ∝ T (Kelvin). So at constant P and n, V/T = constant. If temperature is in Celsius, proportionality is not direct because zero Celsius is not absolute zero. Absolute zero (0 K = -273.15°C) is the theoretical temperature at which volume becomes zero. A graph of V vs T (K) is a straight line through origin.
This question belongs to: Science chemistry
Question #264
The diffusion of gases is explained by:
A. Avogadro's law
B. Charles' law
C. Graham's law
D. Boyle's law
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Correct Answer: Option C

Explanation:
Graham's law of diffusion/effusion states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass. Lighter gases diffuse faster. This law helps in separating isotopes (e.g., ²³⁵U enrichment) and understanding gas behavior. Boyle's and Charles' deal with P-V-T relationships. Avogadro's deals with V and number of moles.
This question belongs to: Science chemistry
Question #265
Which of the following is an example of a negative catalyst?
A. Alcohol in chloroform storage to prevent phosgene formation
B. Pt in SO₂ oxidation
C. Fe in Haber process
D. MnO₂ in H₂O₂ decomposition
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Correct Answer: Option A

Explanation:
A small amount of ethanol (alcohol) is added to chloroform to inhibit its oxidation by air to toxic phosgene (COCl₂) and HCl. Ethanol acts as a negative catalyst (stabilizer) by consuming any formed phosgene. MnO₂, Pt, Fe are positive catalysts. Negative catalysts are also called inhibitors, used to prevent undesirable reactions.
This question belongs to: Science chemistry
Question #266
Enzymes are affected by pH and temperature because they are:
A. Nucleic acids
B. Carbohydrates
C. Proteins
D. Lipids
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Correct Answer: Option C

Explanation:
Enzymes are proteins with complex three-dimensional structures maintained by hydrogen bonds, ionic bonds, and hydrophobic interactions. Extremes of pH or high temperature disrupt these bonds, causing denaturation (loss of structure and function). Each enzyme has an optimum pH and temperature. For example, pepsin works in acidic stomach, trypsin in alkaline intestine.
This question belongs to: Science chemistry
Question #267
In the extraction of zinc from zinc blende (ZnS), the first step is:
A. Leaching with NaOH
B. Electrolysis
C. Smelting with coke
D. Roasting in air
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Correct Answer: Option D

Explanation:
Zinc blende (ZnS) is first concentrated by froth flotation, then roasted in excess air to convert it to ZnO: 2ZnS + 3O₂ → 2ZnO + 2SO₂. ZnO is then reduced with coke at high temperature (smelting) or dissolved in H₂SO₄ and electrolyzed. Roasting is typical for sulfide ores to remove sulfur as SO₂.
This question belongs to: Science chemistry
Question #268
Which of the following is an organic fertilizer?
A. Urea
B. Superphosphate
C. Compost
D. Ammonium nitrate
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Correct Answer: Option C

Explanation:
Compost is decomposed organic matter (plant waste, manure) and is an organic fertilizer. Urea, though organic compound, is considered a synthetic nitrogenous fertilizer when industrially produced. Organic fertilizers are derived from natural sources: manure, bone meal, compost. They improve soil structure. Ammonium nitrate, superphosphate are inorganic/synthetic. Urea is often categorized as synthetic organic.
This question belongs to: Science chemistry
Question #269
Sulphuric acid is used in the preparation of which of the following?
A. Nitric acid (via nitration) and many chemicals
B. Sodium hydroxide
C. Hydrochloric acid
D. Ammonia
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Correct Answer: Option A

Explanation:
Sulphuric acid is a key reagent in many processes: to produce HCl from NaCl, HNO₃ from nitre, fertilizers (superphosphate), and in petroleum refining, pickling, etc. It is also used as a dehydrating agent and catalyst. Ammonia is made by Haber process without H₂SO₄. NaOH is made by electrolysis of brine. H₂SO₄ is known as 'king of chemicals'.
This question belongs to: Science chemistry
Question #270
Hydrochloric acid is produced by the reaction of NaCl with:
A. Concentrated sulphuric acid
B. Sodium hydroxide
C. Ammonia
D. Nitric acid
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Correct Answer: Option A

Explanation:
NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl↑, at low temperature. At high temperature, NaHSO₄ + NaCl → Na₂SO₄ + HCl. This is the laboratory preparation of HCl gas. Industrial production is by direct combination of H₂ and Cl₂. Nitric acid is an oxidizer and would produce chlorine. Sodium hydroxide gives salt and water (neutralization). Ammonia reacts with acid.
This question belongs to: Science chemistry
Question #271
Hydrogen peroxide is used as a rocket propellant because it:
A. Decomposes to release oxygen and steam, providing thrust
B. Is extremely stable
C. Burns in air
D. Is a fuel
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Correct Answer: Option A

Explanation:
High-concentration H₂O₂ (e.g., 80-90%) decomposes rapidly in the presence of a catalyst to produce superheated steam and oxygen: 2H₂O₂ → 2H₂O + O₂ + heat. This generates high-pressure gas used for propulsion (monopropellant) or as oxidizer in bipropellant systems. It is not a fuel; it provides oxygen for combustion. It must be handled carefully due to instability.
This question belongs to: Science chemistry
Question #272
The IUPAC name of methyl alcohol is:
A. Ethanol
B. Propanol
C. Butanol
D. Methanol
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Correct Answer: Option D

Explanation:
Methyl alcohol (CH₃OH) is systematically named methanol (meth- = 1 carbon, -ol = alcohol). Ethanol = C₂H₅OH. Propanol = C₃H₇OH. Butanol = C₄H₉OH. Common name 'methyl alcohol' derives from methane. IUPAC names use alkane stem + 'ol'. Methanol is the simplest alcohol.
This question belongs to: Science chemistry
Question #273
Soap works by forming structures called micelles. The hydrophobic tails dissolve in:
A. The soap dish
B. Water
C. The oily dirt
D. Air
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Correct Answer: Option C

Explanation:
The long hydrocarbon chain (tail) of soap is non-polar and hydrophobic, so it dissolves into the oily/greasy dirt particle. The ionic head (hydrophilic) remains in the water. This forms a micelle around the dirt, emulsifying it and allowing it to be washed away. The tail-dirt interaction is via van der Waals forces.
This question belongs to: Science chemistry
Question #274
Cement mixed with water undergoes an exothermic reaction. The heat evolved is called:
A. Heat of fusion
B. Heat of solution
C. Heat of hydration
D. Heat of combustion
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Correct Answer: Option C

Explanation:
When cement hydrates, it releases heat known as heat of hydration. This exothermic process can cause thermal cracking in massive concrete structures if not controlled. The main compounds C₃S and C₃A have high heat of hydration. For dams, low-heat cement with lower C₃A content is used. Heat of solution is for dissolving, combustion for burning, fusion for melting.
This question belongs to: Science chemistry
Question #275
Teflon's non-stick property is due to:
A. Low surface energy and chemical inertness
B. Its metallic nature
C. Its ability to absorb oil
D. High polarity of C-F bonds
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Correct Answer: Option A

Explanation:
Teflon (PTFE) has a very low coefficient of friction and surface energy because the fluorine atoms form a protective shield around the carbon backbone, making it difficult for other substances to adhere. This is not due to polarity (C-F bonds are polar but the molecule overall is non-polar due to symmetry). It is extremely inert, resisting most chemicals.
This question belongs to: Science chemistry
Question #276
PVC's rigidity in its unplasticized form is due to:
A. Polar C-Cl bonds causing intermolecular attractions
B. Covalent cross-links
C. High molecular weight only
D. Strong hydrogen bonding
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Correct Answer: Option A

Explanation:
PVC has polar C-Cl bonds; the chlorine atoms create dipole-dipole interactions between polymer chains, restricting chain movement and making the material rigid and strong. Adding plasticizers (e.g., phthalates) reduces intermolecular forces, making it flexible. Cross-links are in thermosets, PVC is thermoplastic. High molecular weight contributes but polarity is key.
This question belongs to: Science chemistry
Question #277
Hard water does not produce good lather with soap because it contains:
A. Potassium ions
B. Sodium ions
C. Calcium and magnesium ions
D. Chloride ions
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Correct Answer: Option C

Explanation:
Calcium (Ca²⁺) and magnesium (Mg²⁺) ions react with soap anions to form insoluble precipitates (scum), preventing lather. Sodium and potassium soaps are soluble and lather well. So detergents are preferred in hard water because their calcium/magnesium salts are soluble. Hardness is measured in terms of CaCO₃ equivalent.
This question belongs to: Science chemistry
Question #278
Ozone is used to purify water because it:
A. Is a strong disinfectant and leaves no harmful residue
B. Makes water acidic
C. Adds minerals
D. Adds odor
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Correct Answer: Option A

Explanation:
Ozone (O₃) is a more powerful oxidant than chlorine; it destroys bacteria, viruses, and organic contaminants, and then decomposes to oxygen, leaving no residual taste or toxic disinfection by-products. However, it does not provide lasting protection in distribution pipes, so a small chlorine dose may be added. Ozonation also removes color and odor.
This question belongs to: Science chemistry
Question #279
Which of the following gases contributes to the greenhouse effect?
A. Carbon dioxide
B. Oxygen
C. Nitrogen
D. Hydrogen
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Correct Answer: Option A

Explanation:
CO₂ is a major greenhouse gas that absorbs infrared radiation and re-emits it, warming the atmosphere. Other GHGs: CH₄, N₂O, water vapor, CFCs. N₂ and O₂ are diatomic homonuclear molecules that do not absorb IR and are not GHGs. Hydrogen is not a GHG. The increase in CO₂ due to human activities is driving climate change.
This question belongs to: Science chemistry
Question #280
Gamma rays have the highest penetration power because they:
A. Are slowest
B. Are heaviest
C. Carry positive charge
D. Have no mass and no charge
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Correct Answer: Option D

Explanation:
Gamma rays are electromagnetic waves with no rest mass and no charge, so they do not readily interact with matter via ionization compared to alpha and beta particles. They can penetrate deep into materials, requiring dense lead or thick concrete for shielding. Alpha and beta particles interact strongly via charge, losing energy quickly. Gamma rays are similar to X-rays but from nuclear origin.
This question belongs to: Science chemistry

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