Arrange the following in decreasing order of their basic strength in…

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) (C₂H₅)₂NH

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) C₂H₅NH₂

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)