Arrange the following in decreasing order of their basic strength in aqueous solution

(A) $C_6H_5NH_2$
(B) $C_2H_5NH_2$
(C) $(C_2H_5)_2NH$
(D) $NH_3$

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

The correct answer is Option (1) → (C), (B), (D), (A)

Core Concept:

In aqueous solution, basic strength depends on both electron-donating effect and solvation of the conjugate acid.

Secondary amines are most basic due to strong +I effect and good solvation, followed by primary amines, then ammonia, while aromatic amines are least basic due to resonance.

Option (C) (Câ‚‚Hâ‚…)â‚‚NH

This is a secondary amine where two alkyl groups donate electron density to nitrogen, increasing its ability to accept a proton, and the resulting ion is well stabilised in aqueous medium, making it the strongest base.

Option (B) Câ‚‚Hâ‚…NHâ‚‚

This primary amine has one alkyl group that increases electron density on nitrogen, making it more basic than ammonia but less basic than secondary amines.

Option (D) NH₃

Ammonia lacks electron-donating alkyl groups, so it has lower electron density on nitrogen compared to alkyl amines, resulting in moderate basic strength.

Option (A) C₆H₅NH₂

In aniline, the lone pair on nitrogen participates in resonance with the benzene ring, reducing its availability for protonation, making it the weakest base.

Final Order:

(C) > (B) > (D) > (A)