Question

please explain me this problem with full solutions

Answer 1

in the above question, no resonace is occuring,no M effect is seen so we will directly ponder H effect (hyperconjugation effect), where we see number of alpha H beside cation.

Stability of cation directly proportional to no. of alpha H.
In question 1 we have7 alpha H,
in second question we have 5alpha H,
in 3rd we have1 alpha H,
in last we have 0 alpha H. So maximum alpha H is in que 1st So answer is (a).