Explanation

In

the strongly withdrawing `F_3 C-` group withdraws electrons of the `C-C` bond towards itself. AB a result, the positive charge on C gets intensified and therefore ,

is less stable. On the other hand, in carbocation `F_3 C^(+)- -` lone pair of electrons on each of the three F-atoms overlaps with the empty p-orbital of the carbon atom carrying the positive charge thereby dispersing the positive charge and thus stabilizing the carbocation `Fe_3 C^(+)` relative to


-I-effect of the F atoms destubilizes the carbocation by intensifying the +ve charge.

Back bonding from 2p orbitals of F to empty 2p orbital of C disperses +ve charge