The order of basic strength of amine in aqueous solution is:

The correct answer is Option (1) → \(C_6H_5CH_2NH_2 < C_2H_5NH_2 < (C_2H_5)_3N  < (C_2H_5)_2NH\)

In water the basic strength of an alkylamine is decided by three factors together: the +I effect of the alkyl groups (more groups, more electron density on N), solvation of the ammonium ion by hydrogen bonding (fewer N–H, poorer solvation) and steric hindrance. For ethylamines these combine to give

    \( \ce{(C2H5)2NH} \) > \( \ce{(C2H5)3N} \) > \( \ce{C2H5NH2} \) > \( \ce{NH3} \)

Benzylamine, \( \ce{C6H5CH2NH2} \), is an aliphatic amine (the N is not on the ring), but the phenyl group pulls electrons slightly (−I), so it is weaker than ethylamine: pK_b 4.70 against 3.29 for \( \ce{C2H5NH2} \), 3.25 for \( \ce{(C2H5)3N} \) and 3.00 for \( \ce{(C2H5)2NH} \).

NCERT (2026-27 edition):
Basic Character of Amines – “The order of basic strength in case of methyl substituted amines and ethyl substituted amines in aqueous solution is as follows:
    (C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃
    (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃”

Basic Character of Amines – Table 9.3: pK_b Values of Amines in Aqueous Phase