The order of basicity is I>III>II>IV The lone pair of electrons on N is more readily available for protonation in I and III then in II. Ill contains an oxygen atom which has -I effect due to which it is less basic than I. In compound IV lone pair of e−s on N-atom is contributed towards the aromatic sextet formation and hence is not at all available for protonation. Hence option (b) is correct.
