Chemistry MCQs

Question #81

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Which type of glass is used for making laboratory glassware and cookware due to its high thermal resistance?

A. Soda-lime glass

B. Quartz glass

C. Borosilicate glass

D. Lead crystal glass

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Correct Answer: Option C

Explanation:
Borosilicate glass (e.g., Pyrex) contains boron trioxide (B₂O₃) along with silica, giving it low coefficient of thermal expansion, thus resistant to cracking under temperature changes. Soda-lime glass is ordinary glass, used for bottles, windows. Lead crystal has high refractive index for decorative items. Quartz glass (pure SiO₂) has very high melting point but is expensive. Borosilicate is ideal for beakers, test tubes.

This question belongs to: Science chemistry

Question #82

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Teflon is a polymer of:

A. Styrene

B. Vinyl chloride

C. Ethylene

D. Tetrafluoroethene

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Correct Answer: Option D

Explanation:
Teflon (PTFE) is an addition polymer of tetrafluoroethene (CF₂=CF₂). The polymer has a linear chain of –CF₂–CF₂– units with high C–F bond strength, making it chemically inert and heat resistant. PVC is polymer of vinyl chloride (CH₂=CHCl). Polyethylene comes from ethylene. Polystyrene from styrene. Teflon is used for non-stick coatings, electrical insulation, and chemical containers.

This question belongs to: Science chemistry

Question #83

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Temporary hardness of water can be removed by:

A. Adding calcium sulfate

B. Boiling

C. Adding sodium chloride

D. Filtration

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Correct Answer: Option B

Explanation:
Boiling converts soluble bicarbonates of Ca and Mg to insoluble carbonates: Ca(HCO₃)₂ (heat) → CaCO₃↓ + H₂O + CO₂, which can then be filtered. Permanent hardness (due to sulfates/chlorides) is not removed by boiling; requires washing soda, ion exchange, or calgon. Calcium sulfate addition would increase permanent hardness. Filtration removes solid particles, not dissolved ions.

This question belongs to: Science chemistry

Question #84

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Ozonation as a water purification method has an advantage over chlorination because:

A. It is cheaper

B. It leaves no residual disinfectant

C. It does not produce harmful by-products like trihalomethanes

D. It makes water acidic

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Correct Answer: Option C

Explanation:
Ozone (O₃) is a powerful disinfectant that decomposes to oxygen, leaving no toxic residues or taste. Chlorination can form carcinogenic trihalomethanes (THMs) with organic matter. However, ozone is more expensive, must be generated on-site, and leaves no residual protection in distribution system, often requiring a small chlorine dose. Ozonation also removes color and odor. Both kill bacteria and viruses.

This question belongs to: Science chemistry

Question #85

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Global warming is primarily due to the increase in atmospheric concentration of:

A. Nitrogen

B. Argon

C. Oxygen

D. Carbon dioxide

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Correct Answer: Option D

Explanation:
The enhanced greenhouse effect causing global warming is mainly due to rising CO₂ levels from fossil fuel combustion, deforestation, and industrial processes. Other GHGs like CH₄, N₂O, CFCs also contribute. Oxygen and nitrogen are not greenhouse gases. Argon is noble gas, inert. The atmospheric CO₂ has increased from ~280 ppm (pre-industrial) to over 420 ppm. This leads to climate change, sea level rise, and extreme weather.

This question belongs to: Science chemistry

Question #86

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John Dalton's atomic theory helped explain:

A. Law of multiple proportions

B. Discovery of radioactivity

C. Wave nature of electron

D. Quantum theory

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Correct Answer: Option A

Explanation:
Dalton's atomic theory (1808) provided a framework for the laws of chemical combination—conservation of mass, constant composition, and multiple proportions. The law of multiple proportions states that when two elements form more than one compound, masses of one that combine with fixed mass of the other are in small whole number ratios. Dalton proposed atoms combine in simple whole number ratios to form compounds.

This question belongs to: Science chemistry

Question #87

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Niels Bohr's atomic model successfully explained the spectrum of:

A. Helium atom

B. Oxygen atom

C. Hydrogen atom

D. Carbon atom

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Correct Answer: Option C

Explanation:
Bohr's model (1913) could accurately predict the line spectrum of hydrogen and hydrogen-like ions (single-electron species like He⁺, Li²⁺) by introducing quantized energy levels and angular momentum. It failed for multi-electron atoms due to electron-electron interactions. The model explained the Balmer series of hydrogen. Modern quantum mechanics with Schrödinger equation replaced it. Bohr also introduced the concept of stationary orbits.

This question belongs to: Science chemistry

Question #88

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Which gas law is expressed by P₁V₁/T₁ = P₂V₂/T₂ for a fixed mass of gas?

A. Boyle's law

B. Gay-Lussac's law

C. Charles' law

D. Combined gas law

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Correct Answer: Option D

Explanation:
The combined gas law integrates Boyle's (P₁V₁ = P₂V₂), Charles' (V₁/T₁ = V₂/T₂), and Gay-Lussac's (P₁/T₁ = P₂/T₂) laws into one equation: P₁V₁/T₁ = P₂V₂/T₂ for a fixed amount of gas. It assumes ideal behavior. When one variable is constant, the respective individual law can be derived. For changing conditions, this combined form is useful. For n moles, PV = nRT.

This question belongs to: Science chemistry

Question #89

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Graham's law of diffusion relates rate of diffusion to:

A. Square root of molar mass

B. Temperature

C. Density

D. Pressure

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Correct Answer: Option A

Explanation:
Graham's law: Rate of diffusion/effusion ∝ 1/√M, where M is molar mass. Lighter gases diffuse faster. At same T and P, rates of two gases r₁/r₂ = √(M₂/M₁). Example: NH₃ (17 g/mol) diffuses faster than HCl (36.5 g/mol). This law is used in isotope separation (e.g., ²³⁵UF₆ vs ²³⁸UF₆). The law assumes no intermolecular forces and identical conditions.

This question belongs to: Science chemistry

Question #90

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The role of a catalyst in a chemical reaction is to:

A. Increase the equilibrium constant

B. Provide an alternative pathway with lower activation energy

C. Decrease the enthalpy change

D. Increase the temperature of the reaction

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Correct Answer: Option B

Explanation:
A catalyst lowers the activation energy (Ea) by providing an alternative reaction mechanism, thereby increasing the rate of both forward and reverse reactions equally. It does not affect the equilibrium constant, enthalpy change (ΔH), or the position of equilibrium. It remains chemically unchanged after reaction. Positive catalysts speed up, negative catalysts slow down. Enzymes are biological catalysts.

This question belongs to: Science chemistry

Question #91

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The main impurity present in iron ore obtained from mining is:

A. Alumina

B. Lime

C. Carbon

D. Silica

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Correct Answer: Option D

Explanation:
The chief impurity in iron ores (hematite, magnetite) is silica (SiO₂), which is acidic gangue. In the blast furnace, limestone (CaCO₃) is added as flux; it decomposes to CaO, which combines with silica to form fusible calcium silicate slag: CaO + SiO₂ → CaSiO₃. This slag floats on molten iron and is removed. Alumina may also be present but silica is the primary impurity.

This question belongs to: Science chemistry

Question #92

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In the refining of copper by electrolytic refining, the anode is:

A. Impure copper

B. Graphite

C. Pure copper

D. Platinum

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Correct Answer: Option A

Explanation:
In electrolytic refining of copper, impure copper is used as the anode, a thin sheet of pure copper as the cathode, and CuSO₄ acidified with H₂SO₄ as electrolyte. On passing current, copper dissolves from the anode and pure copper deposits on the cathode. Impurities like gold, silver fall as anode mud. This yields 99.99% pure copper. Similar process for other metals.

This question belongs to: Science chemistry

Question #93

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Organic fertilizers improve soil health primarily by:

A. Killing weeds

B. Increasing organic matter and microbial activity

C. Adding synthetic chemicals

D. Rapidly releasing nitrogen

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Correct Answer: Option B

Explanation:
Organic fertilizers (compost, manure, bone meal) add humus, improving soil structure, water retention, and aeration. They support beneficial microorganisms that slowly decompose organic matter, releasing nutrients gradually. Unlike synthetic fertilizers, they do not cause sudden nutrient spikes or soil acidification. Biofertilizers like Rhizobium fix nitrogen. Organic farming emphasizes sustainability and reduced chemical inputs.

This question belongs to: Science chemistry

Question #94

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Nitric acid is manufactured by Ostwald process. The catalyst used is:

A. V₂O₅

B. Fe

C. Ni

D. Pt-Rh gauze

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Correct Answer: Option D

Explanation:
Ostwald process: Catalytic oxidation of NH₃ with air over a platinum-rhodium gauze catalyst at ~800°C to form NO, then NO₂, finally absorbed in water to give HNO₃. Fe is Haber catalyst for NH₃. V₂O₅ is for SO₂ oxidation. Ni for hydrogenation. Pt-Rh alloy gauze provides high surface area and mechanical strength, reducing cost. Nitric acid is used in fertilizers (ammonium nitrate), explosives, and nitration.

This question belongs to: Science chemistry

Question #95

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Sodium hydroxide is manufactured by the electrolysis of brine (NaCl solution). Which gas is produced at the anode?

A. Nitrogen

B. Hydrogen

C. Chlorine

D. Oxygen

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Correct Answer: Option C

Explanation:
In chlor-alkali process (electrolysis of concentrated NaCl solution), Cl⁻ ions are oxidized at the anode: 2Cl⁻ → Cl₂(g) + 2e⁻ (chlorine gas). At the cathode, H₂O is reduced: 2H₂O + 2e⁻ → H₂(g) + 2OH⁻, producing hydrogen gas and leaving NaOH in solution. The process uses a diaphragm or membrane cell to keep products separate. Chlorine is used for water treatment and PVC.

This question belongs to: Science chemistry

Question #96

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Hydrogen peroxide acts as an oxidizing agent in which reaction?

A. H₂O₂ + Ag₂O → 2Ag + H₂O + O₂

B. H₂O₂ + 2KI + H₂SO₄ → I₂ + K₂SO₄ + 2H₂O

C. H₂O₂ + O₃ → H₂O + 2O₂

D. H₂O₂ + PbS → PbSO₄ + H₂O

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Correct Answer: Option D

Explanation:
In reaction C, H₂O₂ oxidizes PbS (black) to PbSO₄ (white), where oxygen atoms from H₂O₂ are added. H₂O₂ itself is reduced to H₂O. In reaction D, H₂O₂ oxidizes I⁻ to I₂; that is also oxidation. But the most straightforward oxidizing reaction among these is the restoration of old paintings (PbS → PbSO₄). Reaction A: H₂O₂ reduces O₃ (acts as reducing agent). Reaction B: H₂O₂ reduces Ag₂O. H₂O₂ can act as both oxidizing and reducing agent.

This question belongs to: Science chemistry

Question #97

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Methanol is toxic. Ingestion of methanol leads to:

A. Lung cancer

B. Liver cirrhosis

C. Blindness or death

D. Kidney failure

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Correct Answer: Option C

Explanation:
Methanol is metabolized in the body to formaldehyde and formic acid, which are highly toxic and can damage the optic nerve, causing permanent blindness or even death if ingested in significant amounts. Ethanol is used as an antidote because it competitively inhibits methanol metabolism by alcohol dehydrogenase. Methanol is used as industrial solvent and in illegal liquor (hooch) sometimes resulting in mass poisoning.

This question belongs to: Science chemistry

Question #98

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Which of the following is NOT a characteristic of metals?

A. Ductility

B. High thermal conductivity

C. Malleability

D. Brittleness

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Correct Answer: Option D

Explanation:
Brittleness is a property typical of non-metals and metalloids; metals are ductile and malleable, not brittle. Ductility: drawn into wires (gold most ductile). Malleability: beaten into sheets (gold most malleable). Metals also have luster, high thermal and electrical conductivity, and sonorous nature. Brittle substances break easily under stress without significant deformation (e.g., glass, sulfur). Some metals like cast iron are brittle but generally pure metals are not.

This question belongs to: Science chemistry

Question #99

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The reactivity series ranks metals based on their tendency to:

A. Form covalent bonds

B. Lose electrons and form positive ions

C. Accept electrons

D. Absorb hydrogen

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Correct Answer: Option B

Explanation:
Reactivity series orders metals according to their ease of oxidation—i.e., losing electrons to form cations. At the top (K, Na) are strong reducing agents, reacting vigorously with water and acids; at the bottom (Au, Pt) are noble metals, resistant to corrosion. The series helps predict displacement reactions and extraction methods. Mnemonic: 'Please Stop Calling Me A Cute Zebra...' etc.

This question belongs to: Science chemistry

Question #100

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Alloying iron with chromium and nickel produces stainless steel which is resistant to corrosion because:

A. Chromium forms a protective oxide layer

B. Nickel dissolves in iron and prevents reaction

C. Chromium makes iron more reactive

D. Iron becomes non-metal

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Correct Answer: Option A

Explanation:
Stainless steel contains at least 10.5% chromium, which reacts with oxygen to form a thin, adherent, transparent Cr₂O₃ layer (passive film) that prevents further oxidation of the underlying metal. Nickel enhances corrosion resistance and ductility. This self-healing oxide layer makes it 'stainless'. Unlike galvanization, the protection is not sacrificial but barrier-type from the inherent alloy composition.

This question belongs to: Science chemistry

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