Which of the following carbocations is expected to be the most stable?

${\mathrm{NO}}_2$ is present at the ortho- and the para- position of a positive charge.

${\mathrm{NO}}_2$ present at the meta-position of a positive charge is less stable due to the ${\mathrm{e}}^{-}$ withdrawing effect of  $-{\mathrm{NO}}_2$ ($-\mathrm{I}$ effect of ${\mathrm{NO}}_2$) 



${\mathrm{NO}}_2$  present at the ortho- and para- of positive charge (Less stable due to the ${\mathrm{e}}^{-}$ withdrawing effect of $-{\mathrm{NO}}_2$ ($-\mathrm{M}$ effect.)



The positive charge is destabilized by the electron-withdrawing groups.
$-\mathrm{M}$ dominates $-\mathrm{I}$ effect. So, the carbocation which has $-\mathrm{I}$ group is more stable.