−CH3 is the most stable carbocation. The stability of carbocations increases as we go from primary to secondary to tertiary carbons. It is because tertiary carbocations have more inductively donating groups as compared to secondary and primary carbocation. Secondly, in case of tertiary carbocation there are more hyper conjugative structures as compared to secondary and primary carbocation. Hence, the order of stability of carbocations is 3°>2°>1°
