Compare the basicity of aryl amines with alkyl amines.

(N/A) Aryl amines (e.g.,aniline) are much weaker bases than ammonia and alkyl amines.
In aryl amines,the $-NH_2$ group is directly attached to the benzene ring. The unshared electron pair on the nitrogen atom is in conjugation with the benzene ring,which makes it less available for protonation.
As shown in the resonance structures,the electron density on the nitrogen atom decreases due to the delocalization of the lone pair into the benzene ring.
Furthermore,the anilinium ion formed by accepting a proton is less stable than the aniline molecule itself because the resonance stabilization is lost upon protonation.
In contrast,in alkyl amines,the electron-releasing $+I$ effect of the alkyl group increases the electron density on the nitrogen atom,making the lone pair more available for protonation and stabilizing the resulting alkyl ammonium ion.