The decreasing order of basic strength is I > III > II.
Thus I is most basic and II is least basic. The lone pair on nitrogen atom of – NH₂ group is in resonance with benzene ring. Due to this resonance, the electron density is maximum in ortho and para positions. Due to this, the basicity is maximum in I. The electron density is minimum in meta position. Hence, the basicity is minium in II. In the structure III, there is possibility of H bonding between ring nitrogen and the amino group. Hence, III is less basic than I.