31. Which of the following compounds will give a positive Hinsberg test?
a) Ethylamine
b) Diethylamine
c) Triethylamine
d) Methylamine
Answer: a) Ethylamine
Explanation: The Hinsberg test distinguishes primary, secondary, and tertiary amines. Ethylamine, a primary amine, reacts with Hinsberg reagent to form a sulfonamide soluble in alkali, giving a positive test. Secondary and tertiary amines behave differently.
32. What is the product when acetamide is treated with Br₂ and NaOH (Hoffmann bromamide reaction)?
a) Methylamine
b) Ethylamine
c) Aniline
d) Acetone
Answer: a) Methylamine
Explanation: The Hoffmann bromamide reaction converts an amide (acetamide, CH₃CONH₂) to a primary amine with one less carbon atom. In this case, the product is methylamine (CH₃NH₂).
33. Aniline when treated with excess acetic anhydride produces:
a) Acetone
b) Acetanilide
c) Anilinium ion
d) N,N-Diacetylaniline
Answer: b) Acetanilide
Explanation: When aniline is treated with acetic anhydride, it undergoes acetylation to form acetanilide. This reaction protects the amine group and prevents further reactions on the nitrogen atom.
34. Which of the following does not give a positive nitrous acid test?
a) Aniline
b) Methylamine
c) Diethylamine
d) Benzylamine
Answer: c) Diethylamine
Explanation: The nitrous acid test is used to distinguish between primary, secondary, and tertiary amines. Diethylamine (a secondary amine) does not form diazonium salts with nitrous acid and gives a negative result in this test.
35. Which of the following reagents can be used to reduce nitro compounds to amines?
a) Fe/HCl
b) NaOH
c) KMnO₄
d) H₂SO₄
Answer: a) Fe/HCl
Explanation: Nitro compounds are typically reduced to amines using reducing agents like iron filings and hydrochloric acid (Fe/HCl) or other catalytic hydrogenation processes.
36. Which of the following compounds is not prepared by the reduction of a nitro compound?
a) Aniline
b) Phenylhydroxylamine
c) Azobenzene
d) Benzene
Answer: d) Benzene
Explanation: Benzene is not prepared by the reduction of a nitro compound. Compounds like aniline and phenylhydroxylamine are produced from the reduction of nitrobenzene.
37. When aniline reacts with cold HNO₂ in the presence of HCl, the product is:
a) Acetanilide
b) Benzenediazonium chloride
c) Phenol
d) Benzylamine
Answer: b) Benzenediazonium chloride
Explanation: Aniline reacts with cold nitrous acid (generated in situ from NaNO₂ and HCl) to form benzenediazonium chloride (C₆H₅N₂⁺Cl⁻), which is an important intermediate in synthetic organic chemistry.
38. What is the major product when aniline reacts with acetic anhydride?
a) Nitroaniline
b) Acetanilide
c) Benzanilide
d) Acetone
Answer: b) Acetanilide
Explanation: Acetic anhydride reacts with aniline to form acetanilide by acetylating the amino group (-NH₂). This reaction is used to protect the amine group in subsequent reactions.
39. Which of the following nitro compounds is most reactive towards nucleophilic substitution?
a) Nitrobenzene
b) 2,4-Dinitrochlorobenzene
c) m-Nitroaniline
d) p-Nitrotoluene
Answer: b) 2,4-Dinitrochlorobenzene
Explanation: 2,4-Dinitrochlorobenzene is highly reactive towards nucleophilic substitution because the two nitro groups strongly withdraw electron density from the ring, making the carbon bearing the chlorine more susceptible to nucleophilic attack.
40. Which of the following reagents converts aniline into a diazonium salt?
a) HCl and NaNO₂
b) Br₂ and Fe
c) KMnO₄ and NaOH
d) CH₃COOH and NaOH
Answer: a) HCl and NaNO₂
Explanation: Aniline is converted into benzenediazonium chloride by treating it with a mixture of sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at low temperatures (0-5°C).
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