Correct Answer - Lack of delocalisation of `(4n+2)pi` electrons in the cyclic system.

For the given compound, the number of `(pi)`-electrons is 6. By Huckel’s rule,

4n + 2 = 6

4n = 4

n = 1

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is an integer, the given compound is aromatic in nature.

(ii)

For the given compound, the number of π-electrons is 4. By Huckel’s rule,

4n + 2 = 4

4n=2

`n=(1)/(2)`

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…), which is not true for the given compound. Hence, it is not aromatic in nature.

For the given compound, the number of π-electrons is 8.

By Huckel’s rule, 4n+2=8

4n=6

`n=(3)/(2)`

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is not an integer, the given compound is not aromatic in nature.