Arrange the following bases in decreasing order of basicity is
(i) Aniline
(ii) O - nitroaniline
(iii) m- nitroaniline
(iv) p - nitroaniline

Basicity is directly proportional to the $+\mathrm{M},+\mathrm{I}$ effect, but it is inversely proportional to the $-\mathrm{M},-\mathrm{I}$ effect. Aniline is the highest basic because it does not have any group. But the nitro group can show the $-\mathrm{I}$and $-\mathrm{M}$ effect. The nitro group at meta position show only the $-\mathrm{I}$ effect. But at ortho and para position, it will show the $-\mathrm{M},-\mathrm{I}$ effect both. So, the $\mathrm{m}-$nitroaniline is more basic than the $\mathrm{p}-$nitroaniline and $\mathrm{o}-$nitroaniline.

So, the basicity order is :-

Hence, the decreasing order of basicity is $(\mathrm{i}) >(\mathrm{iii})>(\mathrm{iv})>(\mathrm{ii})$.