Question

Which of the following carbonium ion has the
least stability ?

• A. methyl
• B. ethyl
• C. isopropyl
• D. ter-butyl

Answer 1

The correct option is A methyl

Stability of carbonium ion or carbocation depends on the adjacent alkyl groups. Alkyl groups exhibit electron releasing $+I$ effect and hyperconjugative effect which stabilizes the positive charge. $C{H}_3^{+}$ methyl carbonium ion does not have both of these effects, therefore it is the least stable.