Rearrange the following in an increasing order of their basic strenghts :
`C_(6)H_(5)NH_(2),C_(6)H_(5)N(CH_(3))_(2),(C_(6)H_(5))_(2)NH and CH_(3) NH_(2)`

Explanation

(i) Due to delocalization of lone pair of electrons of the N-atom over the benzene ring, all aromatic amines are less basic than alkylamines, i.e., `CH_(3)NH_(2)`.
(ii) Presence of electron donating grous (i.e., `CH_(3)`) on the N-atom increases the basicity of substituted aniline w.r.t. `C_(6)H_(5)NH_(2)`.
(iii) In `(C_(6)H_(5))_(2)NH`, th lone pair of electrons on the N-atom is delocalized over two benzene rings instead of one in `C_(6)H_(5)NH_(2)`, therefore, `(C_(6)H_(5))_(2)NH` is much less basic than `C_(6)H_(5)NH_(2)`.
Combining all the three trends together, the basicitiy of the four amines increases in the order: `(C_(6)H_(5))_(2)NH lt C_(6)H_(5)NH_(2) lt C_(6)H_(5)N(CH_(3))_(2) lt CH_(3)NH_(2)`.