81. Which of the following amines is least basic?
a) Ethylamine
b) Aniline
c) Dimethylamine
d) Benzylamine
Answer: b) Aniline
Explanation: Aniline is less basic than aliphatic amines like ethylamine and dimethylamine because the lone pair of electrons on the nitrogen is delocalized into the aromatic ring, reducing its availability for protonation.
82. Which of the following compounds does not give a positive Hinsberg test?
a) Ethylamine
b) Diethylamine
c) Triethylamine
d) Aniline
Answer: c) Triethylamine
Explanation: Triethylamine, a tertiary amine, does not react with Hinsberg’s reagent and, therefore, does not give a positive Hinsberg test. The test is used to differentiate primary and secondary amines.
83. Which of the following products is obtained when nitrobenzene is reduced by lithium aluminium hydride (LiAlH₄)?
a) Azobenzene
b) Aniline
c) Benzylamine
d) Phenylhydroxylamine
Answer: b) Aniline
Explanation: Lithium aluminium hydride (LiAlH₄) is a strong reducing agent that reduces nitrobenzene to aniline by converting the nitro group (-NO₂) to an amino group (-NH₂).
84. Which of the following amines does not undergo diazotization?
a) Methylamine
b) Aniline
c) p-Toluidine
d) o-Nitroaniline
Answer: a) Methylamine
Explanation: Methylamine, a primary aliphatic amine, does not form a stable diazonium salt. Instead, it reacts with nitrous acid to release nitrogen gas, forming methanol as a byproduct.
85. The basicity of amines in aqueous solution follows which order?
a) NH₃ > CH₃NH₂ > (CH₃)₂NH > (CH₃)₃N
b) (CH₃)₃N > (CH₃)₂NH > CH₃NH₂ > NH₃
c) (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃
d) CH₃NH₂ > NH₃ > (CH₃)₃N > (CH₃)₂NH
Answer: c) (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃
Explanation: In aqueous solution, secondary amines like dimethylamine ((CH₃)₂NH) are the most basic due to better solvation and availability of the lone pair on nitrogen, followed by primary amines, tertiary amines, and ammonia.
86. Which of the following reagents is used to carry out the diazotization of aniline?
a) NaNO₂/HCl at 273 K
b) H₂SO₄/NaNO₃ at 300 K
c) NaOH/H₂O₂
d) Br₂ and FeCl₃
Answer: a) NaNO₂/HCl at 273 K
Explanation: The diazotization of aniline is carried out by treating it with sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at low temperatures (273 K or 0-5°C) to form a diazonium salt.
87. Which of the following amines can be prepared by Gabriel phthalimide synthesis?
a) Methylamine
b) Ethylamine
c) Diethylamine
d) Trimethylamine
Answer: b) Ethylamine
Explanation: The Gabriel phthalimide synthesis is used to prepare primary amines such as ethylamine by treating phthalimide with an alkyl halide, followed by hydrolysis.
88. Which of the following products is obtained when nitrobenzene is reduced with hydrogen and nickel catalyst?
a) Azobenzene
b) Aniline
c) Phenylhydroxylamine
d) Benzylamine
Answer: b) Aniline
Explanation: Nitrobenzene is reduced to aniline using hydrogen (H₂) in the presence of a nickel catalyst (Ni). The nitro group (-NO₂) is fully reduced to an amino group (-NH₂).
89. Which of the following compounds will not react with nitrous acid at low temperatures to form a diazonium salt?
a) Aniline
b) Benzylamine
c) p-Nitroaniline
d) m-Toluidine
Answer: b) Benzylamine
Explanation: Benzylamine, a primary aliphatic amine, does not form a stable diazonium salt with nitrous acid. It decomposes to release nitrogen gas.
90. Which of the following amines undergoes the Sandmeyer reaction?
a) Diethylamine
b) Aniline
c) Benzylamine
d) Ethylamine
Answer: b) Aniline
Explanation: Aniline undergoes diazotization to form a diazonium salt, which can participate in the Sandmeyer reaction, where it reacts with CuCl or CuBr to form chlorobenzene or bromobenzene, respectively.
Leave a comment