Arrange the following in the decreasing order of their basic strength in aqueous solutions: CH3NH2, (CH3)2NH, (CH3)3N, NH3

+I groups, like R groups, increases the electron density on nitrogen which increases the basicity (electron rich is basic) of amine. Of the given amines, more the number of R groups on nitrogen more is the basic nature of amine. Basicity also depends on the steric hindrance. More is the steric hindrance less is the basicity. So, the correct order is (CH3)2NH > CH3NH2 > (CH3)3N > NH3.