Chemistry MCQs

Question #561

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The chemical formula of bleaching powder is:

A. Ca(OH)₂

B. CaSO₄·½H₂O

C. Na₂CO₃·10H₂O

D. CaOCl₂

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Correct Answer: Option D

Explanation:
Bleaching powder is chemically calcium oxychloride, with the formula CaOCl₂. It is produced by the action of chlorine gas on dry slaked lime (Ca(OH)₂). Option A is slaked lime, C is plaster of Paris, and D is washing soda. It is used for disinfecting water and bleaching textiles.

This question belongs to: Science chemistry

Question #562

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Which of the following salts does not contain water of crystallization?

A. Baking soda

B. Washing soda

C. Blue vitriol

D. Gypsum

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Correct Answer: Option A

Explanation:
Baking soda (NaHCO₃) is an anhydrous salt and does not contain water of crystallization. Blue vitriol (CuSO₄·5H₂O), washing soda (Na₂CO₃·10H₂O), and gypsum (CaSO₄·2H₂O) all contain fixed water molecules integrated into their crystal lattice, which gives them their specific shape and color.

This question belongs to: Science chemistry

Question #563

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Plaster of Paris is obtained by heating gypsum at:

A. 473 K

B. 673 K

C. 373 K

D. 573 K

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Correct Answer: Option C

Explanation:
Plaster of Paris (CaSO₄·½H₂O) is formed by heating gypsum (CaSO₄·2H₂O) at 373 K (100°C). This causes it to lose 1.5 molecules of water per formula unit. If heated significantly above 473 K, it loses all water and forms dead burnt plaster (anhydrous CaSO₄), which cannot set with water.

This question belongs to: Science chemistry

Question #564

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Assertion (A): Dry HCl gas does not change the color of dry litmus paper. Reason (R): Acids produce H⁺ ions only in the presence of water.

A. A is true but R is false.

B. Both A and R are true but R is NOT the correct explanation of A.

C. Both A and R are true and R is the correct explanation of A.

D. A is false but R is true.

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Correct Answer: Option C

Explanation:
The acidic behavior of HCl is due to the presence of H⁺ (or H₃O⁺) ions, which are generated only when it dissolves in water. Without moisture, HCl doesn't dissociate to produce H⁺, so it doesn't change the color of dry litmus. Both statements are correct and R explains A.

This question belongs to: Science chemistry

Question #565

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Which of the following is used for softening hard water?

A. Washing soda

B. Baking soda

C. Bleaching powder

D. Plaster of Paris

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Correct Answer: Option A

Explanation:
Washing soda (sodium carbonate, Na₂CO₃) is used to remove permanent hardness of water. It reacts with soluble calcium and magnesium chlorides/sulfates to form insoluble carbonates, which can be filtered out. Baking soda, bleaching powder, and plaster of Paris do not have this water-softening capability.

This question belongs to: Science chemistry

Question #566

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The indicator that is pink in a basic solution and colorless in an acidic solution is:

A. Methyl orange

B. Litmus

C. Turmeric

D. Phenolphthalein

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Correct Answer: Option D

Explanation:
Phenolphthalein is a synthetic indicator that remains colorless in acidic and neutral solutions but turns pink/magenta in basic solutions. Methyl orange is red in acid and yellow in base. Litmus is red in acid and blue in base. Turmeric is yellow in acid and red in base.

This question belongs to: Science chemistry

Question #567

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The ability of metals to be drawn into thin wires is called:

A. Conductivity

B. Sonority

C. Ductility

D. Malleability

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Correct Answer: Option C

Explanation:
Ductility is the property of metals by which they can be drawn into thin wires. Gold, silver, and copper are highly ductile. Malleability is the ability to be beaten into thin sheets. Sonority is the property of producing a ringing sound when struck. Conductivity refers to heat or electricity.

This question belongs to: Science chemistry

Question #568

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Which of the following metals does not react with dilute hydrochloric acid?

A. Zinc

B. Iron

C. Copper

D. Magnesium

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Correct Answer: Option C

Explanation:
Copper is placed below hydrogen in the reactivity series, meaning it cannot displace hydrogen from dilute acids. Therefore, it does not react with dilute HCl. Mg, Fe, and Zn are above hydrogen in the series and react to release H₂ gas, forming their respective chlorides.

This question belongs to: Science chemistry

Question #569

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The most reactive metal among the following is:

A. Gold

B. Copper

C. Silver

D. Potassium

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Correct Answer: Option D

Explanation:
Potassium (K) is an alkali metal placed at the very top of the reactivity series. It reacts violently with water and air, requiring storage in kerosene. Gold, silver, and copper are noble or less reactive metals placed at the bottom of the series, often found in the free state.

This question belongs to: Science chemistry

Question #570

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Galvanization is the process of coating iron with a thin layer of:

A. Tin

B. Copper

C. Silver

D. Zinc

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Correct Answer: Option D

Explanation:
Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. Zinc acts as a sacrificial anode, meaning it will oxidize preferentially to iron, protecting it even if the coating is scratched and the underlying iron is exposed to moisture.

This question belongs to: Science chemistry

Question #571

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Which non-metal is a good conductor of electricity?

A. Graphite

B. Sulphur

C. Iodine

D. Phosphorus

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Correct Answer: Option A

Explanation:
Graphite, an allotrope of carbon, is a good conductor of electricity. This is because each carbon atom is bonded to three others, leaving one free valence electron per atom that is delocalized and can move freely between the layers to conduct electricity, unlike diamond which is an insulator.

This question belongs to: Science chemistry

Question #572

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Assertion (A): Metals are good reducing agents. Reason (R): Metals have a tendency to lose electrons.

A. Both A and R are true but R is NOT the correct explanation of A.

B. A is true but R is false.

C. A is false but R is true.

D. Both A and R are true and R is the correct explanation of A.

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Correct Answer: Option D

Explanation:
Metals have low ionization energies and a strong tendency to lose electrons (undergo oxidation). By losing electrons, they cause the reduction of other substances, making them excellent reducing agents. Both statements are true, and the tendency to lose electrons perfectly explains their role as reducing agents.

This question belongs to: Science chemistry

Question #573

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The chemical process used for extracting a metal from its ore by dissolving it in a suitable reagent is called:

A. Calcination

B. Leaching

C. Smelting

D. Roasting

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Correct Answer: Option B

Explanation:
Leaching is a chemical method of concentration where the powdered ore is treated with a suitable reagent that dissolves the ore but not the impurities. Calcination and roasting are thermal processes, and smelting involves reduction with a chemical reducing agent like carbon at high temperatures.

This question belongs to: Science chemistry

Question #574

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Which of the following metals is preserved in kerosene oil?

A. Calcium

B. Sodium

C. Iron

D. Magnesium

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Correct Answer: Option B

Explanation:
Sodium and potassium are highly reactive alkali metals that react vigorously with oxygen and moisture in the air, potentially catching fire. To prevent accidental fires, they are stored immersed in kerosene oil. Magnesium and calcium do not require such extreme storage conditions.

This question belongs to: Science chemistry

Question #575

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The hardest natural substance known is:

A. Diamond

B. Coal

C. Fullerene

D. Graphite

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Correct Answer: Option A

Explanation:
Diamond is the hardest known natural substance. It consists of each carbon atom covalently bonded to four other carbon atoms in a rigid tetrahedral 3D lattice, making it extremely hard. Graphite is soft due to its layered structure with weak van der Waals forces between layers.

This question belongs to: Science chemistry

Question #576

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Which gas is the main constituent of biogas and natural gas?

A. Methane

B. Ethane

C. Propane

D. Butane

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Correct Answer: Option A

Explanation:
Methane (CH₄) is the primary component of both natural gas (about 70-90%) and biogas (about 50-75%). It is the simplest alkane and a clean-burning fossil fuel. Ethane, propane, and butane are present in smaller amounts in natural gas but are not the main constituent.

This question belongs to: Science chemistry

Question #577

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The process of converting unsaturated hydrocarbons into saturated hydrocarbons by adding hydrogen is called:

A. Polymerization

B. Substitution

C. Halogenation

D. Hydrogenation

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Correct Answer: Option D

Explanation:
Hydrogenation is the addition of hydrogen to unsaturated compounds (like alkenes or alkynes) in the presence of a catalyst (like Ni, Pd, or Pt) to form saturated compounds (alkanes). For example, ethene + H₂ → ethane. This process is widely used in the food industry to solidify vegetable oils.

This question belongs to: Science chemistry

Question #578

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Which of the following is used as a solvent?

A. All of the above

B. Ethanoic acid

C. Ethyl ethanoate

D. Ethanol

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Correct Answer: Option A

Explanation:
Ethanol is a versatile solvent used in medicines like tinctures and perfumes. Ethanoic acid (glacial) can act as a solvent for many organic compounds. Ethyl ethanoate is an excellent solvent for fats, resins, and plastics, often used in nail polish removers and industrial paints.

This question belongs to: Science chemistry

Question #579

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Soap molecules have two ends with different properties. They are:

A. Lipophobic and hydrophobic

B. Hydrophobic and hydrophilic

C. Both A and B

D. Hydrophilic and lipophilic

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Correct Answer: Option C

Explanation:
A soap molecule has a long hydrocarbon chain which is hydrophobic (water-repelling) or lipophilic (fat-loving), and an ionic head (usually -COO⁻Na⁺) which is hydrophilic (water-loving) or lipophobic (fat-repelling). Both A and B correctly describe these dual properties essential for cleaning action.

This question belongs to: Science chemistry

Question #580

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The reaction of an alcohol with a carboxylic acid in the presence of an acid catalyst to form an ester is called:

A. Esterification

B. Saponification

C. Fermentation

D. Hydrogenation

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Correct Answer: Option A

Explanation:
Esterification is the chemical reaction where a carboxylic acid reacts with an alcohol in the presence of a strong acid catalyst (like conc. H₂SO₄) to produce an ester and water. Saponification is the reverse process, involving the alkaline hydrolysis of esters to form soap and glycerol.

This question belongs to: Science chemistry

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