140. In what approximate pH range can the human body function?
[UPSC NDA — 2024]
(A) 6.8–7.2
(B) 7.0–7.8
(C) 6.5–7.5
(D) 7.5–8.0
Answer: (B) 7.0–7.8
Explanation: The exam cites a broad physiological range around neutrality and mild alkalinity. In particular, healthy arterial blood is regulated much more tightly, typically about pH 7.35–7.45. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
139. Milk of magnesia consists mainly of what?
[UPSC NDA — 2024]
(A) Magnesium bicarbonate
(B) Magnesium carbonate
(C) Magnesium sulphate
(D) Magnesium hydroxide
Answer: (D) Magnesium hydroxide
Explanation: Milk of magnesia is an aqueous suspension of Mg(OH)2. It acts as a mild antacid and, in higher doses, a laxative. Chemical structure, bonding and surrounding conditions determine why the stated choice is correct.
138. Which straight-chain alkane has molecular formula C9H20?
[SSC CGL — 2024]
(A) Nonane
(B) Nonadecane
(C) Dodecane
(D) Icosane
Answer: (A) Nonane
Explanation: An acyclic saturated alkane has formula CnH2n+2. For nine carbon atoms, that becomes C9H20, called nonane. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
137. Which is a saturated hydrocarbon?
[SSC CGL — 2024]
(A) C2H4
(B) C3H8
(C) C6H6
(D) C4H8
Answer: (B) C3H8
Explanation: Propane, C3H8, contains only carbon–carbon single bonds and fits the alkane formula CnH2n+2. The others contain unsaturation or aromatic bonding. The carbon skeleton and degree of unsaturation influence reactions and observable physical properties.
136. Which researchers described the peroxide effect in anti-Markovnikov addition in 1933?
[SSC CGL — 2024]
(A) Liebig and Wöhler
(B) Kharasch and Mayo
(C) Bachrach and Hoffmann
(D) Cadogan and Campos
Answer: (B) Kharasch and Mayo
Explanation: Morris Kharasch and Frank Mayo studied radical addition reactions affected by peroxides. In suitable conditions HBr can add to alkenes contrary to Markovnikov orientation. The structure and bonding of water-related compounds largely determine their physical and chemical properties.
135. Which of these carboxylic acids is strongest?
[SSC CGL — 2024]
(A) C3H7COOH
(B) CH3COOH
(C) C2H5COOH
(D) HCOOH
Answer: (D) HCOOH
Explanation: Formic acid is stronger than the listed alkyl-substituted carboxylic acids because alkyl electron donation weakens acidity. It lacks an electron-donating alkyl group. Identifying each acid requires distinguishing its chemical name from the everyday source mentioned.
134. Which carbon allotrope was discovered by Curl, Kroto and Smalley in 1985?
[SSC CGL — 2024]
(A) Lonsdaleite
(B) Fullerene
(C) Carbophene
(D) Graphene
Answer: (B) Fullerene
Explanation: The researchers reported buckminsterfullerene C60, a cage-like carbon allotrope, in 1985. The discovery opened extensive fullerene and nanocarbon research. Changes in carbon bonding and crystal arrangement can transform electrical and mechanical behaviour dramatically.
133. Palladium deposited on barium sulphate is associated with which named catalyst?
[SSC CGL — 2024]
(A) Aldol catalyst
(B) Cannizzaro catalyst
(C) Rosenmund catalyst
(D) Hillman catalyst
Answer: (C) Rosenmund catalyst
Explanation: The Rosenmund catalyst is poisoned palladium supported on barium sulphate. It is used to hydrogenate acyl chlorides selectively to aldehydes. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
132. Which carboxylic acid has the formula CH3CH2CH2COOH?
[SSC CGL — 2024]
(A) Methanoic acid
(B) Ethanoic acid
(C) Propionic acid
(D) Butyric acid
Answer: (D) Butyric acid
Explanation: The four-carbon straight-chain carboxylic acid is butanoic acid, traditionally butyric acid. It contains one terminal carboxyl group. The carbon skeleton and degree of unsaturation influence reactions and observable physical properties.
131. Water gas contains which pair of gases?
[UPSC NDA — 2024]
(A) CO2 and H2
(B) CO and H2
(C) CO2 and H2O
(D) CO and H2O
Answer: (B) CO and H2
Explanation: Water gas is mainly carbon monoxide mixed with hydrogen. It is produced by reacting steam with hot carbon, creating a combustible gaseous mixture. Hydrogen participates in many compounds whose reactivity differs markedly with the bonded elements.
