The increasing order of basicity of the given compounds is

(CH 3 ) 2 NH > CH 3 NH 2 > (CH 3 ) 3 N > C 6 H 5 NH 2

Due to the +I effect of alkyl groups the electron density on nitrogen increases and thus the availability of the lone pair of electrons to proton increases and hence the basicity of amines also increases. So aliphatic amines are more basic than aniline.

In case of tertiary amine (CH 3 ) 3 N, the covering of alkyl groups over nitrogen atom from all sides makes the approach and bonding by a proton relatively difficult, hence the basicity decreases. Electron withdrawing (C 6 H 5 –) groups decreases electron density on nitrogen atom and thereby decreasing basicity.