Which of the following carbocations is expected to be the most...

${NO}_{2}$ is present at the ortho- and the para- position of a positive charge.

${NO}_{2}$ present at the meta-position of a positive charge is less stable due to the ${e}^{-}$ withdrawing effect of $- {NO}_{2}$ ($- I$ effect of ${NO}_{2}$)



${NO}_{2}$ present at the ortho- and para- of positive charge (Less stable due to the ${e}^{-}$ withdrawing effect of $- {NO}_{2}$ ($- M$ effect.)



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