Correct order of stability of carbocation given below is :-

(1) i > ii > iii > iv        (2) ii > iii > i > iv       (3) ii > i > iii > iv           (4) i > iii > ii > iv

Dear Student,

The Stability of Carbo-cation depends on 3 factors:

1. Neighbouring Carbon atoms (providing +I Effect and Hyper-conjugation).
2. Neighbouring Carbon-Carbon multiple bonds (providing Resonance-effect).
3. Neighbouring atoms with Lone-pair of electrons (providing Resonance-effect).

Now, in this case the deciding/main factor of stability is Resonance-effect, as there are Carbon-Carbon multiple bonds in all the cases.

• The most number of Resonating structures will be present in Benzyl Carbo-cation so this will be the most stable.
• Now comes the the Allylic Carbo-cation which has 2 stabilizing factors namely Resonance and +I effects, which makes it the second most stable Carbo-cation (as resonance effect is less than that in Benzyl Carbo-cation).
• Now, the third most stable Carbo-cation is Cyclopropyl Carbo-cation as it is stabilized by Resonance effect.
• And the least stable Carbo-cation is Vinylic Carbo-cation as there is no resonance effect in this case.

So, the Stability order of Carbo-cation is (ii) > (iii) > (i) > (iv).

Therefore, option (2) is correct.

Hope this information clears your doubts about the topic.

Keep asking!!

Regards