MHTCET 22 Apr 2025 Shift 2 Paper

Concept:Basicity of amines depends on the availability of the lone pair on nitrogen for protonation.A weaker base has a higher $\mathrm{p}K_b$ value.Explanation:In aniline, $C_6H_5NH_2$, the lone pair on nitrogen is delocalised into the benzene ring through resonance.This makes the lone pair less available for donation, so aniline is the weakest base among the given amines.Aliphatic amines like $(\mathrm{CH}_3)_3\mathrm{N}$ and $(\mathrm{CH}_3)_2\mathrm{NH}$ are stronger bases due to the electron-donating inductive effect of methyl groups.Benzylamine, $C_6H_5CH_2NH_2$, has no direct resonance between the ring and the nitrogen lone pair, so it remains more basic than aniline.Since basicity decreases as $\mathrm{p}K_b$ increases, the amine with the highest $\mathrm{p}K_b$ is the weakest base, which is aniline.Answer:$C_6H_5NH_2$ (aniline) – Option C.