100. Which of the following aqueous solutions cannot conduct electricity appreciably?
[UPSC NDA — 2022]
(A) Copper sulphate
(B) Sodium chloride
(C) Sugar
(D) Sodium hydroxide
Answer: (C) Sugar
Explanation: Sugar dissolves as neutral molecules and provides almost no charge carriers. The other solutes release mobile ions and behave as electrolytes. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
99. Which acid is usually cited as responsible for an acidic bee sting?
[UPSC NDA — 2022]
(A) Tartaric acid
(B) Citric acid
(C) Ethanoic acid
(D) Methanoic acid
Answer: (D) Methanoic acid
Explanation: Methanoic acid, or formic acid, is the traditional school-text answer. Actual bee venom is a complex mixture including peptides and enzymes. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
98. Which salt lacks water of crystallisation?
[UPSC NDA — 2022]
(A) Potassium permanganate
(B) Blue vitriol
(C) Washing soda
(D) Mohr’s salt
Answer: (A) Potassium permanganate
Explanation: Potassium permanganate KMnO4 crystallises without fixed water of crystallisation. Blue vitriol, washing soda and Mohr’s salt are well-known hydrated crystalline salts. The elemental composition and oxidation state help distinguish related sulphur-containing chemicals.
97. Which statement about urea fertiliser is incorrect?
[UPSC NDA — 2022]
(A) It is a phosphorus fertiliser
(B) It can improve soil fertility
(C) It can be made from NH3 and CO2
(D) It has high nitrogen content
Answer: (A) It is a phosphorus fertiliser
Explanation: Urea, CO(NH2)2, is a concentrated nitrogen fertiliser, not a phosphorus source. It is produced industrially using ammonia and carbon dioxide. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
96. Which kind of hydrocarbon burns with a yellow, sooty flame more readily?
[UPSC CDS — 2022]
(A) Saturated hydrocarbon
(B) Unsaturated hydrocarbon
(C) Completely oxygenated compound
(D) Only water-containing fuel
Answer: (B) Unsaturated hydrocarbon
Explanation: Unsaturated hydrocarbons generally have a higher carbon-to-hydrogen ratio and may burn with a luminous smoky flame if oxygen is insufficient. Soot consists of incompletely combusted carbon. Hydrogen participates in many compounds whose reactivity differs markedly with the bonded elements.
95. What forms when calcium carbonate reacts with dissolved carbon dioxide and water?
[SSC CGL — 2022]
(A) Calcium oxide
(B) Calcium hydroxide
(C) Hydrochloric acid
(D) Calcium hydrogen carbonate
Answer: (D) Calcium hydrogen carbonate
Explanation: Calcium carbonate dissolves more readily in carbon-dioxide-rich water through formation of aqueous calcium hydrogen carbonate, Ca(HCO3)2. This equilibrium contributes to temporary hardness of natural water. Water solubility and hydration are often as important as composition in their practical use.
94. Which statements are correct?
1. All bases are alkalis.
2. Alkalis dissolve in water.
3. Alkalis may be slippery, bitter and corrosive.
[UPSC CDS — 2021]
(A) 1 only
(B) 1 and 3 only
(C) 2 and 3 only
(D) 3 only
Answer: (C) 2 and 3 only
Explanation: Alkalis are bases soluble in water, so every alkali is a base but not every base is an alkali. Concentrated alkali solutions are chemically hazardous. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
93. Which statements about universal indicator are correct?
1. It mixes several indicators.
2. Its color varies with hydrogen ion concentration.
3. It determines exact titration end points for every acid-base system.
[UPSC CDS — 2021]
(A) 1 only
(B) 1 and 2 only
(C) 2 and 3 only
(D) 1, 2 and 3
Answer: (B) 1 and 2 only
Explanation: Universal indicator combines dyes to display a range of pH values. It supplies approximate acidity or alkalinity but does not replace a suitable titration indicator for precise end-point detection. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
92. Which acid is associated with the stinging hairs of nettles?
[UPSC CDS — 2021]
(A) Methanoic acid
(B) Citric acid
(C) Tartaric acid
(D) Acetic acid
Answer: (A) Methanoic acid
Explanation: Methanoic acid is also called formic acid and is traditionally associated with nettle stings. The irritation results from chemicals delivered by the hairs into the skin. Organic acids share acidic behaviour but differ in molecular structure, biological origins and uses.
91. Which naturally occurring acid is commonly associated with tomatoes?
[UPSC CDS — 2021]
(A) Acetic acid
(B) Citric acid
(C) Oxalic acid
(D) Tartaric acid
Answer: (C) Oxalic acid
Explanation: This exam associates tomatoes with oxalic acid. Tomatoes also contain substantial citric and malic acids, so the particular exam’s comparison matters. Identifying each acid requires distinguishing its chemical name from the everyday source mentioned.
