(CH3)3

+

C

or tert-butyl cation is the most stable of all the given cations. The stability is due to the presence of three methyl groups attached to the carbocation centre. The hydrogens in the methyl group, by hyperconjugation, diminish the electron deficiency (+ve charge) on the carbocation and hence, stabilize it.

In tert-butyl cation the no. of such H atoms which are capable of hyperconjugation is maximum. Thus, it is most stable. In short, greater the no. of α-H more stable will be the carbocation.