Arrange the following amines in increasing order of their basic strength in the gaseous phase

$ (A)\text{C}_6\text{H}_5\text{NH}_2 $
$ (B)\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 $
$ (C)\text{(CH}_3)_3\text{N} $
$ (D)\text{CH}_3\text{NH}_2 $

Choose the correct answer from the options given below:

(A), (B), (D), (C)

The correct answer is Option (2) → (A), (B), (D), (C)

In aniline or other arylamines, the -$NH_2$ group is attached directly to the benzene ring. It results in the unshared electron pair on nitrogen atom to be in conjugation with the benzene ring and thus making it less available for protonation. Aniline is least basic.

$\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 $ (Benzylamine) – More basic than aniline since lone pair is not involved in resonance but electron-donating benzyl group slightly increases basicity

The basic nature of aliphatic amines should increase with increase in the number of alkyl groups. This trend is followed in the gaseous phase. The order of basicity of amines in the gaseous phase follows the expected order: tertiary amine > secondary amine > primary amine > Aniline

Order of basicity in increasing order is A, B, D, C