110. What chemical change can quickly fill certain vehicle airbags with gas?
[UPSC NDA — 2023]
(A) Decomposition of sodium azide to nitrogen
(B) Sublimation of dry ice
(C) Reduction of CO2 to CO
(D) Conversion of CO2 to carbon monoxide
Answer: (A) Decomposition of sodium azide to nitrogen
Explanation: Traditional airbag inflators used rapid sodium azide decomposition to generate nitrogen gas. The released gas expands the bag within milliseconds after impact. Nitrogen compounds are particularly important for agriculture because plants need nitrogen for protein synthesis.
109. Which statement correctly compares diamond with graphite?
[UPSC CDS — 2023]
(A) They have similar physical properties
(B) Diamond is hard, whereas graphite is slippery
(C) Both are good electrical insulators
(D) They possess the same crystal structure
Answer: (B) Diamond is hard, whereas graphite is slippery
Explanation: Although both are carbon allotropes, diamond has a rigid tetrahedral network and is exceptionally hard. Graphite has layered hexagonal sheets that slide over each other readily. Changes in carbon bonding and crystal arrangement can transform electrical and mechanical behaviour dramatically.
108. Which chemical is used to disinfect drinking water?
[SSC MTS (2022 cycle) — 2023]
(A) Chlorine
(B) Ethanol
(C) Phosphorus
(D) Teflon
Answer: (A) Chlorine
Explanation: Chlorination introduces chlorine-derived disinfecting species, particularly hypochlorous acid, into water. They inactivate many disease-causing microorganisms and can leave a protective residual in distribution systems. Halogens lie in group 17 and tend to gain electrons when reacting with metals.
107. Which compound is commonly used as an antacid for stomach acidity?
[SSC MTS (2022 cycle) — 2023]
(A) Iodoform
(B) Morphine
(C) Chlorine
(D) Magnesium hydroxide
Answer: (D) Magnesium hydroxide
Explanation: Magnesium hydroxide, also called milk of magnesia, reacts with excess stomach hydrochloric acid to form magnesium chloride and water. It is a mild base used for acid neutralisation. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
106. Which statement best describes the behavior of oxides of non-metals with water?
[UPSC CDS — 2022]
(A) They produce basic oxides
(B) They generally give acidic solutions
(C) They produce only neutral oxides
(D) They always form hydroxides
Answer: (B) They generally give acidic solutions
Explanation: Many non-metal oxides, such as carbon dioxide and sulphur dioxide, yield acids when dissolved in water. The rule has exceptions for neutral oxides like carbon monoxide. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
105. Milk of magnesia, used for indigestion, is a what?
[UPSC CDS — 2022]
(A) Strong base
(B) Mild base
(C) Strong acid
(D) Mild acid
Answer: (B) Mild base
Explanation: Milk of magnesia is a suspension of magnesium hydroxide, a sparingly soluble base. It neutralises excess gastric acid and therefore serves as an antacid. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
104. Litmus indicator is obtained from which organism?
[UPSC CDS — 2022]
(A) Protozoa
(B) Virus
(C) Lichen
(D) Saccharomyces
Answer: (C) Lichen
Explanation: Litmus is a mixture of natural dyes obtained from certain lichens. In acid it turns red; in alkaline solution it becomes blue. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
103. The fluid injected by stinging nettle hairs is conventionally identified as what?
[UPSC CDS — 2022]
(A) Methanoic acid
(B) Tartaric acid
(C) Hydrochloric acid
(D) Sulphuric acid
Answer: (A) Methanoic acid
Explanation: Methanoic or formic acid is the expected school-level answer. Nettle stinging hairs inject irritating compounds into skin and produce a sharp burning sensation. Identifying each acid requires distinguishing its chemical name from the everyday source mentioned.
102. Methanoic acid is normally associated with which source?
[UPSC CDS — 2022]
(A) Muscles
(B) Urine
(C) Ant stings
(D) Human brain
Answer: (C) Ant stings
Explanation: Methanoic acid is named formic acid from the Latin word for ant. It is associated with the defensive secretions of certain ants. Organic acids share acidic behaviour but differ in molecular structure, biological origins and uses.
101. Which mineral acid is present in human gastric juice?
[UPSC CDS — 2022]
(A) Hydrochloric acid
(B) Lactic acid
(C) Uric acid
(D) Methanoic acid
Answer: (A) Hydrochloric acid
Explanation: Gastric juice contains hydrochloric acid secreted by stomach cells. The acidic medium activates pepsinogen, supports protein digestion and restricts many harmful microorganisms. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
