Basicity $\propto$ electron pair intensity on nitrogen.
(III) Refer image .1 No resonance and $+ I$ effect from both sides $\therefore $ most basic.
(II) Refer image.2 Nitrogen do not involve in resonance $\therefore $ more basic.
(I) Refer image.3 Nitrogen lone pair is involved in resonance.
Therefore less available for donation. . . less basic.
(IV) Refer image. 4
$6 \pi e^{-}$, Aromatic nitrogen lone pair participating in aromaticity $\therefore $ less available for donation.
$\therefore $ least basic.
$\therefore $ III > II > I > IV (Basicity order)
