If u are referring to the carbocations of n-butyl, sec-butyl,
and t-butyl, the most stable is the one that has the most alkyl
groups attached to the positively charged carbon atom. In this
case:
- n-butyl has only 1 alkyl group attached
- sec-butyl has 2 alkyl groups attached
- t-butyl has 3 alkyl groups attached
Therefore, t-butyl is the most stable carbocation