Chemistry MCQs

Question #201

Share Report

Which of the following is a saturated hydrocarbon?

A. Benzene

B. Ethene

C. Propyne

D. Ethane

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Ethane (C₂H₆) is an alkane with single bonds, thus saturated. Ethene (C₂H₄) is an alkene (double bond), propyne (C₃H₄) is an alkyne (triple bond), benzene (C₆H₆) has delocalized π electrons—all unsaturated. Saturated compounds contain only C-C single bonds and maximum possible hydrogen. They undergo substitution reactions.

This question belongs to: Science chemistry

Question #202

Share Report

Petroleum is separated into fractions by:

A. Crystallization

B. Fractional distillation

C. Filtration

D. Sublimation

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Crude petroleum is heated and the vapors are passed through a fractionating column where they condense at different levels according to boiling points. Fractions: petrol (40-120°C), kerosene (150-250°C), diesel (250-350°C), lubricating oil, etc. This is a continuous process. The column has trays and maintains temperature gradient. Simple distillation cannot separate close boiling mixtures.

This question belongs to: Science chemistry

Question #203

Share Report

LPG has an added odorant (ethyl mercaptan) to:

A. Improve engine performance

B. Increase calorific value

C. Detect leakage

D. Reduce combustion temperature

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
LPG (propane/butane) is odorless. A small amount of strong-smelling mercaptan (ethanethiol) is added to help detect gas leaks, preventing accidents. Natural gas also has odorant. Mercaptans contain sulfur, and their smell is detectable at very low concentrations. Calorific value, temperature, performance are unaffected. Safety is primary.

This question belongs to: Science chemistry

Question #204

Share Report

The calorific value of a fuel is measured in a:

A. Thermometer

B. Calorimeter

C. Voltmeter

D. Barometer

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Calorific value is determined using a bomb calorimeter, where a known mass of fuel is burnt in excess oxygen in a sealed bomb, and the heat released is absorbed by a known mass of water. Temperature rise is measured. Corrections for cooling, wire, and acid formation are applied. Units: kJ/kg or kJ/mol. The bomb calorimeter works at constant volume.

This question belongs to: Science chemistry

Question #205

Share Report

Which electrolyte is used in the electroplating of silver?

A. NaCl solution

B. CuSO₄ solution

C. AgNO₃ solution

D. AgCl solution

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
For silver electroplating, the electrolyte is typically a solution of silver cyanide (AgCN) in excess potassium cyanide or silver nitrate (AgNO₃). AgNO₃ with proper complexing agents can be used. CuSO₄ is for copper plating. NaCl is not suitable. The anode is pure silver, cathode is the article. Silver ions migrate to cathode and are reduced to metal.

This question belongs to: Science chemistry

Question #206

Share Report

A gas at STP occupies 22.4 L. If pressure is doubled and temperature is doubled, the volume becomes:

A. 44.8 L

B. 22.4 L

C. 5.6 L

D. 11.2 L

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Combined gas law: P₁V₁/T₁ = P₂V₂/T₂. Given P₂ = 2P₁, T₂ = 2T₁. So V₂ = V₁ × (P₁/P₂) × (T₂/T₁) = 22.4 × (1/2) × (2/1) = 22.4 L. Pressure increase tries to halve volume, temperature increase tries to double volume; they cancel out. So volume remains unchanged. This assumes ideal behavior.

This question belongs to: Science chemistry

Question #207

Share Report

Which of the following is a catalytic process used in industry?

A. Solvay process

B. Hall-Héroult process

C. Haber process

D. Bayer's process

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Haber process synthesizes ammonia using iron catalyst. Solvay process for soda ash uses no solid catalyst but involves reactions with CO₂ and ammonia. Bayer's process for alumina uses NaOH, no catalyst. Hall-Héroult process is electrolytic for aluminium. Catalysis is key in many industrial processes: Contact (V₂O₅), Ostwald (Pt), hydrogenation (Ni).

This question belongs to: Science chemistry

Question #208

Share Report

During the extraction of aluminium by Hall-Héroult process, cryolite (Na₃AlF₆) is added to alumina to:

A. Prevent corrosion

B. Lower the melting point and increase conductivity

C. Act as catalyst

D. Increase the yield of aluminium

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Alumina has a very high melting point (~2050°C). Cryolite (and fluorspar) is mixed to form a molten mixture with lower melting point (~950°C) and better electrical conductivity, enabling electrolytic reduction. The electrolyte is a solution of alumina in molten cryolite. Carbon anodes are consumed. This reduces energy consumption.

This question belongs to: Science chemistry

Question #209

Share Report

Urea is produced by the reaction of ammonia with:

A. Nitric acid

B. Carbon dioxide

C. Sulfuric acid

D. Phosphoric acid

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Urea is synthesized by reacting ammonia and carbon dioxide under high pressure and temperature: 2NH₃ + CO₂ → NH₂COONH₄ (ammonium carbamate) → (NH₂)₂CO + H₂O. This is the Bosch-Meiser urea process. It is the most concentrated solid nitrogenous fertilizer. Urea is also used in animal feed, plastics, and pharmaceuticals.

This question belongs to: Science chemistry

Question #210

Share Report

Which of the following is an example of a chemical change?

A. Cutting of wood

B. Melting of wax

C. Burning of candle

D. Freezing of water

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Burning of a candle involves combustion of wax (hydrocarbons) with oxygen to produce CO₂ and H₂O, a chemical change. The melting of wax is a physical change. Cutting wood is physical (size change). Freezing water is physical (state change). A chemical change results in new substances with different properties. Often irreversible.

This question belongs to: Science chemistry

Question #211

Share Report

The separation technique that uses the difference in boiling points of liquids is:

A. Sublimation

B. Magnetic separation

C. Filtration

D. Distillation

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Distillation separates liquids based on their different boiling points. The mixture is heated; the component with lower boiling point vaporizes first, is condensed and collected. Fractional distillation is used for smaller boiling point differences. Filtration separates solids from liquids. Sublimation separates sublimable solids. Magnetic separates magnetic substances.

This question belongs to: Science chemistry

Question #212

Share Report

An atom has mass number 31 and 16 neutrons. Its atomic number is:

A. 31

B. 47

C. 16

D. 15

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Mass number (A) = protons (Z) + neutrons (N). So Z = A - N = 31 - 16 = 15. This is phosphorus (P). Atomic number 15, mass number 31. It has 15 protons and 15 electrons. Number of neutrons = 16. Isotope notation: ³¹₁₅P.

This question belongs to: Science chemistry

Question #213

Share Report

The ionic bond is formed by:

A. Sharing of electrons by one atom only

B. Mutual sharing of electrons

C. Complete transfer of electrons

D. Sharing of protons

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Ionic (electrovalent) bond is formed by complete transfer of one or more valence electrons from a metal (low ionization energy) to a non-metal (high electron affinity), resulting in oppositely charged ions held by electrostatic forces. Example: Na → Na⁺ + e⁻; Cl + e⁻ → Cl⁻; Na⁺Cl⁻. Covalent bond involves sharing. Coordinate bond involves donation.

This question belongs to: Science chemistry

Question #214

Share Report

The element with highest ionization energy in the second period is:

A. Beryllium

B. Neon

C. Lithium

D. Fluorine

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Ionization energy generally increases across a period due to increasing nuclear charge. Neon (noble gas) has the highest ionization energy in period 2 because of its stable filled octet (2s²2p⁶). Removing an electron requires enormous energy. Fluorine is next highest. Lithium has lowest. Noble gases have very high IE values, making them inert.

This question belongs to: Science chemistry

Question #215

Share Report

Which of the following is a decomposition reaction used in black and white photography?

A. 2H₂O → 2H₂ + O₂

B. 2AgCl → 2Ag + Cl₂

C. CaCO₃ → CaO + CO₂

D. 2AgBr → 2Ag + Br₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Silver bromide (AgBr) decomposes on exposure to light (photochemical decomposition) forming silver and bromine: 2AgBr(s) → 2Ag(s) + Br₂(g). This is used in photographic films to capture images. AgCl also light-sensitive but AgBr is primarily used. Calcium carbonate decomposition is thermal. Water electrolysis is electric decomposition.

This question belongs to: Science chemistry

Question #216

Share Report

A solution turns phenolphthalein pink. Which of the following could it be?

A. Lemon juice

B. Soap solution

C. Vinegar

D. Hydrochloric acid

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Soap solution is basic, pH > 8.3, so it turns phenolphthalein pink. Lemon juice (citric acid) and vinegar (acetic acid) are acidic, pH < 7, phenolphthalein remains colorless. Hydrochloric acid is strongly acidic, colorless. Phenolphthalein indicator is colorless in acidic and neutral, pink in alkaline solutions. It is used in titrations.

This question belongs to: Science chemistry

Question #217

Share Report

Which of the following metals does NOT react with dilute acids to produce hydrogen?

A. Zinc

B. Iron

C. Copper

D. Magnesium

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids (non-oxidizing acids like HCl or H₂SO₄). Magnesium, zinc, and iron are above hydrogen and react to produce H₂ gas. However, copper reacts with oxidizing acids like HNO₃ and hot conc. H₂SO₄, but not to produce H₂—they produce NO₂/SO₂.

This question belongs to: Science chemistry

Question #218

Share Report

Brass is an alloy of:

A. Aluminium and copper

B. Copper and zinc

C. Copper and tin

D. Iron and carbon

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Brass: Cu + Zn. Bronze: Cu + Sn. Steel: Fe + C. Duralumin: Al + Cu + Mg + Mn. Brass is corrosion-resistant and used in plumbing, musical instruments. Zinc content varies (5-45%). Brass with higher zinc is stronger but less ductile. Some brasses contain small amounts of other elements.

This question belongs to: Science chemistry

Question #219

Share Report

Diamond is a poor conductor of electricity because:

A. It has free electrons

B. It has a layered structure

C. All four valence electrons are involved in covalent bonding, no free electrons

D. It is made of carbon

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
In diamond, each carbon is sp³ hybridized and forms four covalent bonds, using all valence electrons. There are no delocalized electrons; thus it cannot conduct electricity. Graphite, with sp² hybridization, has one delocalized electron per carbon, making it a conductor. Diamond is an electrical insulator but excellent thermal conductor.

This question belongs to: Science chemistry

Question #220

Share Report

The main gas present in CNG is:

A. Butane

B. Propane

C. Ethane

D. Methane

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Compressed Natural Gas (CNG) is primarily methane (CH₄). It is stored at high pressure (200-250 bar). It is used as a vehicular fuel and for cooking. LPG is primarily propane and butane. CNG is cleaner, produces less CO₂ per unit energy, and is safer in leaks as methane is lighter than air. It has high octane rating.

This question belongs to: Science chemistry

Practice Questions

More Science Topics