Give the correct order of decreasing basicity of the following compounds:
(a) I > II > III > IV                      (b) IV > III > II > I
(c) IV > I > II> III                       (d) III > II > I > IV

Basicity decreases due to :
1)Presence of electron withdrawing group
2) delocalization  of lone pair on N  due to resonance with benzene ring.
In this question
Structure IV  --N is bonded to sp3 carbon - No resonance
Structure I   --Lone pair are delocalized in phenyl group
Structure II   --Lone pair are delocalized in two phenyl groups
Structure III   --Lone pair are delocalized in 3 phenyl groups
Now you can arrange them in basicity order