30. Which compound contains no sp²-hybridised carbon atom?
[AIEEE Chemistry — 2004]
(A) Acetone
(B) Acetamide
(C) Acetonitrile
(D) Acetic acid
Answer: (C) Acetonitrile
Explanation: In acetonitrile, CH₃C≡N, the nitrile carbon is sp-hybridised and the methyl carbon is sp³-hybridised. Acetone, acetamide and acetic acid each contain a carbonyl carbon, which is normally trigonal planar and sp²-hybridised.
29. Which of these compounds is not chiral?
[AIEEE Chemistry — 2004]
(A) 1-Chloropentane
(B) 3-Chloro-2-methylpentane
(C) 1-Chloro-2-methylpentane
(D) 2-Chloropentane
Answer: (A) 1-Chloropentane
Explanation: 1-Chloropentane has no carbon attached to four different substituents and is therefore achiral. Each of the other named molecules contains at least one stereogenic carbon under the indicated structure. Chirality here depends on substituent differences, not merely the presence of chlorine.
28. What happens when ethyl acetate is mixed with an ordinary aqueous sodium chloride solution?
[AIEEE Chemistry — 2004]
(A) Ethyl acetate and sodium chloride remain chemically unchanged
(B) Chloromethane and sodium propanoate form
(C) Acetyl chloride and ethanol form
(D) Sodium acetate and ethanol form immediately
Answer: (A) Ethyl acetate and sodium chloride remain chemically unchanged
Explanation: Ordinary aqueous sodium chloride does not provide the strong acid or base required to hydrolyse ethyl acetate rapidly. The ester therefore remains chemically unchanged; dissolved salt can instead reduce its solubility in the water layer through a salting-out effect.
27. Which listed carbonyl compound undergoes the Cannizzaro reaction in concentrated alkali?
[AIEEE Chemistry — 2004]
(A) Phenol
(B) Benzoic acid
(C) Butanal
(D) Benzaldehyde
Answer: (D) Benzaldehyde
Explanation: Benzaldehyde has no alpha hydrogen and can undergo Cannizzaro disproportionation in concentrated hydroxide solution. One aldehyde molecule is oxidised to a benzoate ion as another is reduced to benzyl alcohol. Butanal possesses alpha hydrogen and generally favours aldol chemistry.
26. Which organic compound can be reduced to its corresponding hydrocarbon by the Clemmensen method?
[AIEEE Chemistry — 2004]
(A) Ethyl acetate
(B) Butan-2-one
(C) Acetamide
(D) Acetic acid
Answer: (B) Butan-2-one
Explanation: Clemmensen reduction converts an aldehyde or ketone carbonyl into a methylene group using zinc amalgam and strong hydrochloric acid. Butan-2-one is therefore converted into butane. Esters, amides and carboxylic acids do not ordinarily undergo the same direct transformation.
25. Why are sodium sulphate and sodium silicate added to detergent washing powder?
1. To keep it dry;
2. To maintain alkalinity.
[UPSC CSE Prelims — 2003]
(A) Only statement 1
(B) Only statement 2
(C) Both statements 1 and 2
(D) Neither statement 1 nor 2
Answer: (C) Both statements 1 and 2
Explanation: Sodium sulphate acts as a bulking and flow-supporting ingredient in washing powders, helping the mixture remain dry and manageable. Sodium silicate contributes alkalinity and detergent-building properties. Both functions support the performance and storage stability of detergent formulations, making both statements correct.
24. Which alkane produces just one monochloro derivative on UV-initiated chlorination?
[AIEEE Chemistry — 2003]
(A) n-Pentane
(B) Isopentane
(C) Neopentane
(D) Propane
Answer: (C) Neopentane
Explanation: All twelve hydrogen atoms of neopentane occupy equivalent methyl positions because of its highly symmetrical structure. Substituting any one of them with chlorine gives the same constitutional product. The other listed alkanes have nonequivalent hydrogens and produce more than one monochloro isomer.
23. By which reagent can 1-butene be converted into butane?
[AIEEE Chemistry — 2003]
(A) Sn/HCl
(B) Zn-Hg
(C) H₂/Pd
(D) Zn/HCl
Answer: (C) H₂/Pd
Explanation: Catalytic hydrogenation adds molecular hydrogen across the carbon-carbon double bond of but-1-ene. Palladium facilitates formation of the saturated alkane butane. The other reagent systems commonly serve reduction purposes but do not represent the usual catalytic hydrogenation of an isolated alkene.
22. What is the reactivity order of aniline
(I), benzene
(II) and nitrobenzene
(III) towards electrophilic aromatic substitution?
[AIPMT Chemistry — 2003]
(A) III > II > I
(B) II > III > I
(C) I < II > III
(D) I > II > III
Answer: (D) I > II > III
Explanation: Aniline’s amino group donates electron density to the aromatic ring by resonance, activating it toward electrophilic substitution. Nitrobenzene is strongly deactivated by its electron-withdrawing nitro group, while benzene is intermediate. Accordingly, the reactivity order is aniline, benzene and then nitrobenzene.
21. Formation of lactic acid by cyanohydrin addition to ethanal and hydrolysis yields which optical composition?
[AIPMT Chemistry — 2003]
(A) Pure D-isomer
(B) Pure L-isomer
(C) Equal D and L isomers
(D) 20% D and 80% L
Answer: (C) Equal D and L isomers
Explanation: The planar carbonyl carbon of ethanal can be attacked by cyanide from either face with equal probability when no chiral influence is present. Hydrolysis then yields a racemic lactic acid mixture containing equal amounts of the two enantiomers, designated D and L.
