The ring systems having following characteristics are aromatic.
(i) Planar ring containing conjugated `pi` bonds .
(ii) Complete delocalisation of the `pi` -electron in ring system i.e. , each atom in the ring has unhybridised p-orbital , and
(iii) Presence of `(4n+2)pi`-electrons in the ring where n is an integer(n = 0, 1, 2, .......) [Huckel rule]. Using this information classify the following compounds as aromatic/non-aromatic.

Explanation

A = Planar ring, all atoms (C and N) of the ring are up hybridized. It has `6` delocalized `pi` electrons and follows Huckel's rule. Therefore, it is aromatic.
B = Has `6 pi` electrons, but the delocalization stops at `sp^(3)` hybridized `CH_(2)` carbon. Therefore, it is not aromatic.
C = `6` delocalized `pi` electrons (`4 pi`) electrons of the two double bonds and `2` unshared electrons on negatively charged carbon) in a planar ring, follows Huckel's rule. It is aromatic.
D = Has only `4` delocalized `pi`-electrons. It is Anti-aromatic.
E = `6` delocalized `pi`-electrons follows Huckel's rule. `pi` electrons are in `sp^(2)` hybridized orbitals, conjugation all over the ring because of positively charged carbon. The ring is planar. Therefore, it is aromatic.
F = Follows Huckel's rule, has ` 2pi` electrons i.e., (`4n + 2`) `pi`-electrons where (`n = 0`), delocalized `pi`-electrons. Therefore, it is aromatic
G = `8 pi` electrons, does not follow Huckel's rule i.e., (`4n + 2`) `pi`-electrons rule. It is non aromatic.