Chemistry MCQs

Question #221

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Electrolysis is a process in which:

A. Light energy is absorbed

B. Heat energy is converted to electrical energy

C. Chemical energy is converted to electrical energy

D. Electrical energy is used to cause a non-spontaneous chemical reaction

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Correct Answer: Option D

Explanation:
Electrolysis uses an external electric current to drive a chemical reaction that would not occur spontaneously. Example: 2NaCl (molten) → 2Na + Cl₂. Option A describes a galvanic cell. Electrolytic cells require energy input. Electroplating, extraction of reactive metals (Al, Na), and production of chemicals (NaOH, Cl₂) rely on electrolysis.

This question belongs to: Science chemistry

Question #222

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The relationship between volume and temperature for a fixed mass of gas at constant pressure was given by:

A. Charles

B. Boyle

C. Gay-Lussac

D. Avogadro

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Correct Answer: Option A

Explanation:
Jacques Charles formulated the law: V ∝ T at constant P. Hence Charles' law. Gay-Lussac's law relates pressure and temperature at constant volume. Boyle's law: pressure-volume at constant temperature. Avogadro's law: volume-moles at same T & P. Charles also was a pioneer in ballooning.

This question belongs to: Science chemistry

Question #223

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Which catalyst is used in the conversion of vegetable oil to vanaspati ghee?

A. Al

B. Cu

C. Ni

D. Zn

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Correct Answer: Option C

Explanation:
Finely divided nickel is used as catalyst for hydrogenation of unsaturated oils to saturated fats. Platinum and palladium can also be used but are more expensive. The reaction occurs at about 150°C with H₂ gas. Nickel catalyst is prepared by reducing NiO with H₂. This is an important industrial process for making margarine and shortenings.

This question belongs to: Science chemistry

Question #224

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The metal that is extracted by the electrolytic reduction of its fused salt is:

A. Sodium

B. Iron

C. Copper

D. Zinc

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Correct Answer: Option A

Explanation:
Highly reactive metals (K, Na, Ca, Mg, Al) are extracted by electrolysis of their fused (molten) salts because chemical reducing agents cannot reduce their ores. For sodium, Down's process: electrolysis of molten NaCl with CaCl₂ to lower melting point. Iron is extracted by smelting (blast furnace). Copper and zinc can be extracted by reduction with coke or electrolytic refining of impure metal.

This question belongs to: Science chemistry

Question #225

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NPK fertilizer with grade 15-15-15 means it contains:

A. 15% N, 15% P, 15% K by mass

B. 15% N, 15% P₂O₅, 15% K₂O

C. 15 kg of each nutrient

D. 15% total nutrients

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Correct Answer: Option B

Explanation:
Fertilizer grade is expressed as N-P₂O₅-K₂O percentage by mass. So 15-15-15 means 15% N, 15% P₂O₅ (not elemental P), and 15% K₂O (not elemental K). To convert P₂O₅ to P, multiply by 0.44; K₂O to K by 0.83. This is a balanced compound fertilizer providing all three primary macronutrients.

This question belongs to: Science chemistry

Question #226

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Ammonia is used in the manufacture of which fertilizer?

A. Urea

B. Superphosphate

C. Potassium sulfate

D. Gypsum

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Correct Answer: Option A

Explanation:
Ammonia reacts with CO₂ to produce urea: 2NH₃ + CO₂ → NH₂COONH₄ → (NH₂)₂CO + H₂O. It is also used to make ammonium sulfate, ammonium nitrate, DAP, etc. Superphosphate is made by treating rock phosphate with sulfuric acid; no ammonia. Gypsum is CaSO₄·2H₂O. Potassium sulfate is K₂SO₄. Ammonia is a key intermediate in nitrogenous fertilizers.

This question belongs to: Science chemistry

Question #227

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The acid used in the pickling of metals to remove oxide layers is:

A. Hydrochloric acid

B. Nitric acid

C. Acetic acid

D. Carbonic acid

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Correct Answer: Option A

Explanation:
Hydrochloric acid (HCl) is commonly used for pickling (cleaning) steel to remove rust and scale (iron oxides) before further processing like galvanizing or plating. Reaction: Fe₂O₃ + 6HCl → 2FeCl₃ + 3H₂O. Sulfuric acid is also used. Nitric acid is an oxidizer and would passivate some metals. Acetic acid is too weak.

This question belongs to: Science chemistry

Question #228

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The main constituent of biogas is:

A. Hydrogen

B. Ethane

C. Nitrogen

D. Methane

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Correct Answer: Option D

Explanation:
Biogas is produced by anaerobic decomposition of organic matter (cow dung, agricultural waste) and typically contains 50-70% methane (CH₄), 30-40% CO₂, and traces of H₂S, NH₃, and H₂. Methane provides the fuel value. Biogas is a renewable fuel used for cooking and electricity generation. The slurry is good manure.

This question belongs to: Science chemistry

Question #229

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Which of the following is a natural polymer?

A. Teflon

B. Nylon

C. PVC

D. Starch

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Correct Answer: Option D

Explanation:
Starch (polysaccharide) is a natural polymer made from glucose units. It is found in plants. Cellulose, proteins, natural rubber are natural polymers. PVC, nylon, Teflon are synthetic polymers. Natural polymers are biodegradable and renewable. Starch is used as food, in paper, and bioplastics. Synthetic polymers are often derived from petrochemicals.

This question belongs to: Science chemistry

Question #230

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The process of removing permanent hardness of water by adding washing soda is based on:

A. Evaporation

B. Oxidation

C. Precipitation of calcium and magnesium carbonates

D. Ion exchange only

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Correct Answer: Option C

Explanation:
Washing soda (Na₂CO₃) reacts with Ca²⁺ and Mg²⁺ ions in hard water to form insoluble carbonates: Ca²⁺ + Na₂CO₃ → CaCO₃↓ + 2Na⁺. Similarly MgCO₃. These precipitates are removed, softening the water. Ion exchange uses zeolites or resins. Boiling removes only temporary hardness. Distillation is expensive.

This question belongs to: Science chemistry

Question #231

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Which of the following is a major air pollutant responsible for acid rain?

A. N₂

B. SO₂

C. O₂

D. CO

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Correct Answer: Option B

Explanation:
Sulfur dioxide (SO₂) from burning of fossil fuels (coal, oil) reacts with water vapor to form sulfurous and sulfuric acids, causing acid rain. Nitrogen oxides (NOx) also contribute. CO is a toxic gas but does not form strong acid; O₂ and N₂ are normal atmospheric gases. Acid rain damages ecosystems, buildings, and soil.

This question belongs to: Science chemistry

Question #232

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Radioactive isotope Cobalt-60 is used for:

A. Cancer therapy

B. Tracer in agriculture

C. Dating fossils

D. Smoke detectors

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Correct Answer: Option A

Explanation:
Cobalt-60 emits high-energy gamma rays used in radiotherapy (teletherapy) to treat cancers by damaging DNA of malignant cells. Carbon-14 is used for radiocarbon dating. Americium-241 is used in smoke detectors. Phosphorus-32 is used as tracer. Radiotherapy must be carefully targeted to minimize damage to healthy tissue.

This question belongs to: Science chemistry

Question #233

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Which scientist proposed the law of conservation of mass?

A. J. J. Thomson

B. Antoine Lavoisier

C. John Dalton

D. Ernest Rutherford

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Correct Answer: Option B

Explanation:
Antoine Lavoisier is known as the father of modern chemistry and formulated the law of conservation of mass—mass is neither created nor destroyed in a chemical reaction. Dalton's atomic theory supported this law. Thomson discovered electron. Rutherford discovered nucleus. Lavoisier also named oxygen and hydrogen and established the role of oxygen in combustion.

This question belongs to: Science chemistry

Question #234

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Atomic number of an element is 17. It belongs to which group and period?

A. Group 17, Period 3

B. Group 16, Period 2

C. Group 1, Period 3

D. Group 18, Period 3

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Correct Answer: Option A

Explanation:
Atomic number 17 is chlorine. Electronic configuration: 2,8,7. Period number = number of shells = 3. Group number = 10 + valence electrons (for p-block elements) = 10+7 = 17. Hence Group 17 (halogens), Period 3. Group 1 has 1 valence electron, Group 16 has 6, Group 18 has 8 (except He). Simple method: period = number of shells.

This question belongs to: Science chemistry

Question #235

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Which of the following pairs will form an ionic bond?

A. Potassium and fluorine

B. Nitrogen and hydrogen

C. Hydrogen and chlorine

D. Carbon and oxygen

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Correct Answer: Option A

Explanation:
Potassium (metal, low EN) and fluorine (most electronegative non-metal) have large EN difference (~3.2), leading to electron transfer and ionic bond (KF). Carbon-oxygen form polar covalent (CO₂). H-Cl polar covalent. Nitrogen-hydrogen covalent (NH₃). Ionic bonds form between metals of Group 1, 2 and non-metals of Group 16, 17.

This question belongs to: Science chemistry

Question #236

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In the periodic table, metalloids are found:

A. Only in the f-block

B. In the s-block

C. Along the zigzag line separating metals and non-metals

D. Only in group 18

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Correct Answer: Option C

Explanation:
Metalloids (B, Si, Ge, As, Sb, Te) are located along the staircase line on the right side of the p-block, dividing metals from non-metals. They exhibit intermediate properties: semiconductors, brittle, can form alloys. They are in groups 13-17. The s-block contains reactive metals. Group 18 contains noble gases. f-block contains lanthanides and actinides.

This question belongs to: Science chemistry

Question #237

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Which of the following processes involves a chemical change?

A. Boiling of water

B. Magnetization of iron

C. Fermentation of sugar

D. Melting of ice

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Correct Answer: Option C

Explanation:
Fermentation of sugar (glucose) by yeast produces ethanol and carbon dioxide—new substances are formed, so it's a chemical change. Melting, boiling are physical state changes. Magnetization aligns domains but does not change chemical composition. Chemical changes involve breaking and forming of bonds. Indicators: gas evolution, color change, heat, precipitate.

This question belongs to: Science chemistry

Question #238

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The technique used to separate colors in a dye is:

A. Distillation

B. Filtration

C. Centrifugation

D. Chromatography

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Correct Answer: Option D

Explanation:
Chromatography separates components of a mixture based on differential affinities between a stationary phase and a mobile phase. In paper chromatography, dyes separate due to different rates of movement. Distillation is for liquids, centrifugation for density-based separation, filtration for solids from liquids. Chromatography is used in forensics, drug testing, and food coloring analysis.

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Question #239

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Which subatomic particle has a mass of approximately 1.67 × 10⁻²⁷ kg and no charge?

A. Neutron

B. Electron

C. Positron

D. Proton

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Correct Answer: Option A

Explanation:
Neutron has mass approximately equal to proton (1.675 × 10⁻²⁷ kg) and no electric charge. Proton mass ~1.673 × 10⁻²⁷ kg, positive charge. Electron mass ~9.11 × 10⁻³¹ kg, negative charge. Positron is the antiparticle of electron, same mass, positive charge. Neutron's neutrality makes it important for nuclear stability.

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Question #240

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Isotopes are used in which of the following applications?

A. Building materials

B. Treatment of goitre

C. As fuel in thermal power plants

D. Chemical fertilizers

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Correct Answer: Option B

Explanation:
Iodine-131 is a radioactive isotope used to treat thyroid disorders including goitre and cancer. Carbon-14 for dating, Cobalt-60 for cancer therapy, Uranium-235 as fuel in nuclear reactors. Non-radioactive isotopes are used as tracers. Goitre is often caused by iodine deficiency, but radioactive iodine can be used therapeutically.

This question belongs to: Science chemistry

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