Non-Metals & Compounds — Chemistry

Q.1

WBCS Prelims 2021

Dry ice means

A. Ice at – 23°C

B. Ice at 4°C

C. Solid SO2

D. Solid CO2

Explanation

Why Correct: Dry ice is the solid form of carbon dioxide (CO2) that sublimates directly from solid to gas at -78.5°C without passing through a liquid phase.
Distractor Analysis: Ice at -23°C is just ordinary water ice at a specific subzero temperature. Ice at 4°C refers to water near its maximum density point. Solid SO2 (sulfur dioxide) exists but is not called dry ice; it melts at -72°C and boils at -10°C.
Takeaway: Dry ice creates dense white fog when exposed to air because cold CO2 gas condenses water vapor, unlike regular ice which melts into liquid water.

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Q.2

WBCS Prelims 2020

Graphite, carbon and diamonds are

A. isotopes

B. isomers

C. isotones

D. allotropes

Explanation

Why Correct: Graphite, diamond, and amorphous carbon are allotropes of carbon—different structural forms of the same element in the same physical state.
Distractor Analysis: Isotopes are atoms of the same element with different neutron numbers, like carbon-12 and carbon-14. Isomers are compounds with the same molecular formula but different arrangements, common in organic chemistry. Isotones are nuclides with the same neutron number but different proton numbers, like boron-12 and carbon-13.
Takeaway: Allotropes exist only for elements, not compounds; sulfur has rhombic and monoclinic allotropes, while oxygen has O2 and O3 (ozone).

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Q.3

WBCS Prelims 2018

Bleaching action of chlorine is by

A. decomposition

B. hydrolysis

C. reduction

D. oxidation

Explanation

Why Correct: Chlorine bleaches by oxidizing colored organic compounds, breaking chromophores through addition of oxygen or removal of hydrogen.
Distractor Analysis: Decomposition refers to breaking down into simpler substances, not the bleaching mechanism. Hydrolysis involves water splitting a compound, which chlorine undergoes but doesn't cause bleaching. Reduction involves gain of electrons, opposite of chlorine's oxidizing action.
Takeaway: Sulfur dioxide bleaches by reduction, while hydrogen peroxide and chlorine bleach by oxidation.

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Q.4

WBCS Prelims 2016

Which among the following is called ‘Laughing Gas’ popularly ?

A. Nitric oxide

B. Nitrous oxide

C. Nitrogen penta oxide

D. Nitrogen

Explanation

Why Correct: Nitrous oxide (N2O) produces euphoria and uncontrollable laughter when inhaled, leading to its common name 'laughing gas'.
Distractor Analysis: Nitric oxide (NO) is a signaling molecule in blood vessels. Nitrogen pentoxide (N2O5) is a solid oxidizing agent. Nitrogen (N2) is the diatomic gas that makes up 78% of Earth's atmosphere.
Takeaway: Nitrous oxide is also used as an anesthetic in dentistry and as a propellant in whipped cream dispensers.

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Q.5

WBCS Prelims 2014

The most abundant rare gas in the atmosphere is

A. Helium

B. Neon

C. Argon

D. Xenon

Explanation

Why Correct: Argon constitutes about 0.93% of Earth's atmosphere by volume, making it the most abundant noble gas, primarily produced from the radioactive decay of potassium-40.
Distractor Analysis: Helium is the second most abundant noble gas in the universe but scarce in Earth's atmosphere at about 0.0005%. Neon is present at about 0.0018% and gives orange-red glow in neon signs. Xenon is a trace gas at about 0.000009% and is used in high-intensity lamps and anesthesia.
Takeaway: Nitrogen (78%) and oxygen (21%) together make up 99% of dry air, with argon being the third most abundant gas overall.

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Q.6

WBCS Prelims 2009

Fullerene is

A. An allotrope of carbon

B. A synonym for carborundum

C. Artificial emery

D. A compound of carbon

Explanation

Why Correct: Fullerene is a molecular allotrope of carbon composed of carbon atoms arranged in hollow spheres, tubes, or ellipsoids, with C60 (buckminsterfullerene) being the most common.
Distractor Analysis: Carborundum is silicon carbide, an abrasive compound. Artificial emery is synthetic aluminum oxide used as an abrasive. Compounds of carbon include organic molecules like methane or inorganic ones like carbon dioxide, but fullerene is an elemental form.
Takeaway: Other allotropes of carbon include graphite, diamond, graphene, and amorphous carbon.

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Q.7

WBCS Prelims 2005

Oxygen was discovered by

A. Priestley

B. Lavoisier

C. Charles

D. Boyle

Explanation

Why Correct: Joseph Priestley isolated oxygen in 1774 by heating mercuric oxide and collecting the gas over mercury.
Distractor Analysis: Antoine Lavoisier named oxygen and explained its role in combustion. Jacques Charles discovered the direct proportionality between gas volume and temperature. Robert Boyle established the inverse relationship between gas pressure and volume.
Takeaway: Carl Wilhelm Scheele independently discovered oxygen around 1772 but published after Priestley, leading to historical priority disputes.

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Q.8

WBCS Prelims 2000

Dry ice is made up of

A. Water

B. ChlorineWater & Marine Sciences

C. Hydrocarbon

D. Carbon dioxide

Explanation

Why Correct: Dry ice is solid carbon dioxide (CO2) that sublimates at -78.5°C, used for cooling and stage effects.
Distractor Analysis: Water freezes into ordinary ice at 0°C. Chlorine is a greenish-yellow toxic gas used in water treatment and plastics. Hydrocarbons are organic compounds like methane or octane, consisting solely of hydrogen and carbon atoms.
Takeaway: Sublimation describes the phase change from solid directly to gas, which dry ice exhibits without passing through a liquid phase.

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Q.9

WBCS Prelims 2000

Water gas is a mixture of

A. Carbon monoxide and Hydrogen

B. Carbon di-oxide and Hydrogen

C. Carbon monoxide and Nitrogen

D. Carbon di-oxide and Nitrogen

Explanation

Why Correct: Water gas consists of carbon monoxide (CO) and hydrogen (H2) in roughly equal volumes, produced by reacting steam with hot carbon.
Distractor Analysis: Carbon dioxide and hydrogen form synthesis gas after the water-gas shift reaction. Carbon monoxide and nitrogen are components of producer gas, which includes nitrogen from air. Carbon dioxide and nitrogen are major constituents of flue gases from combustion.
Takeaway: Producer gas contains nitrogen from air, making it less calorific than water gas, which burns with a hotter, cleaner flame.

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Q.10

WBCS Prelims 2001

Chlorine is not a constituent of

A. DDT

B. chlorophyll

C. chloroform

D. bleaching powder

Explanation

Why Correct: Chlorophyll contains magnesium at its center (Mg2+ in porphyrin ring) with carbon, hydrogen, oxygen, and nitrogen atoms, but no chlorine.
Distractor Analysis: DDT (dichloro-diphenyl-trichloroethane) contains multiple chlorine atoms. Chloroform (CHCl3) has three chlorine atoms. Bleaching powder (Ca(OCl)Cl) contains hypochlorite and chloride ions.
Takeaway: Hemoglobin contains iron (Fe2+) at its center, while chlorophyll contains magnesium (Mg2+), making them structurally analogous pigments with different metal ions.

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