120. Which statement about commonly occurring acids is incorrect?
[UPSC CDS — 2023]
(A) Gastric juice contains hydrochloric acid
(B) Vinegar contains acetic acid
(C) Tamarind paste is known mainly for oxalic acid
(D) Citrus fruits supply citric and ascorbic acids
Answer: (C) Tamarind paste is known mainly for oxalic acid
Explanation: Tamarind is notably rich in tartaric acid rather than oxalic acid. The other statements correctly associate stomach juice, vinegar and citrus fruits with characteristic acids. Identifying each acid requires distinguishing its chemical name from the everyday source mentioned.
119. Which acid may a goldsmith use for cleaning gold and silver objects?
[UPSC NDA — 2023]
(A) Sulphuric acid
(B) Nitric acid
(C) Hydrochloric acid
(D) Phosphoric acid
Answer: (B) Nitric acid
Explanation: Nitric acid is used in metal finishing and can dissolve silver and many base metals, while elemental gold resists nitric acid alone. Controlled treatments require specialist precautions. Solubility and the formation of mobile ions explain several familiar reactions of salts.
118. Why do copper sulphate crystals lose their blue colour when heated?
[UPSC NDA — 2023]
(A) Loss of oxygen
(B) Loss of nitrogen
(C) Loss of water
(D) Loss of hydrogen
Answer: (C) Loss of water
Explanation: Hydrated copper sulphate is blue, while anhydrous copper sulphate is nearly white. Heating removes coordinated and lattice water and changes the environment of copper ions. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
117. Which compound is also known as olefiant gas?
[SSC CGL — 2023]
(A) Ethylene
(B) 1-Pentene
(C) Methane
(D) Butane
Answer: (A) Ethylene
Explanation: Olefiant gas is ethene, commonly called ethylene, with formula C2H4. It has a double bond and is an important industrial building block. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
116. Organic compounds with an oxygen atom between two alkyl groups belong to which class?
[SSC CGL — 2023]
(A) Alcohols
(B) Aldehydes
(C) Ketones
(D) Ethers
Answer: (D) Ethers
Explanation: An ether has the general structure R–O–R′. In contrast, alcohols contain an –OH group, aldehydes a terminal carbonyl and ketones an internal carbonyl. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
115. Which boiling-point statements are correct?
I. Chloroform boils around 334 K.
II. Methane boils around 111 K.
[SSC CGL — 2023]
(A) Only I
(B) Neither
(C) Only II
(D) Both I and II
Answer: (D) Both I and II
Explanation: Chloroform boils near 61°C, around 334 K, and methane near −162°C, about 111 K. The large difference reflects molecular mass and intermolecular interactions. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
114. What is the molecular formula of propene?
[SSC CGL — 2023]
(A) C2H4
(B) C3H4
(C) C3H6
(D) C2H2
Answer: (C) C3H6
Explanation: Propene contains three carbon atoms and one carbon–carbon double bond. Acyclic alkenes follow formula CnH2n, giving C3H6. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
113. Complete burning of ethanol in oxygen primarily produces which products?
[SSC CGL — 2023]
(A) Water and heat alone
(B) Carbon dioxide, water and energy
(C) Carbon dioxide and water without energy
(D) Carbon dioxide alone
Answer: (B) Carbon dioxide, water and energy
Explanation: Ethanol combustion is exothermic: C2H5OH + 3O2 → 2CO2 + 3H2O. The reaction releases heat and may emit light in a flame. The carbon skeleton and degree of unsaturation influence reactions and observable physical properties.
112. Unsaturated hydrocarbons commonly burn with which flame colour under smoky conditions?
[SSC CGL — 2023]
(A) Blue
(B) Red
(C) Green
(D) Yellow
Answer: (D) Yellow
Explanation: Unsaturated hydrocarbons often burn with a luminous yellow sooty flame when oxygen supply is limited. Glowing carbon particles give the yellow colour. The carbon skeleton and degree of unsaturation influence reactions and observable physical properties.
111. Which industrial process is widely used for manufacturing ammonia?
[UPSC NDA — 2023]
(A) Ostwald process
(B) Haber–Bosch process
(C) Electric furnace process
(D) Electrolysis process
Answer: (B) Haber–Bosch process
Explanation: The Haber–Bosch process reacts nitrogen and hydrogen under pressure over an iron-based catalyst. The product ammonia is fundamental to nitrogen fertiliser production. Nitrogen compounds are particularly important for agriculture because plants need nitrogen for protein synthesis.
