1 Cyclopentadienyl cation

It is not a aromatic compound because it has $4 \pi$ electron and does not follow Huckel's rule.
2 Cyclo-octatetra-ene

It is also an anti-aromatic compound because it does follow Huckel's rule is $(4 n+2) \pi e^{-}$.

It is an aromatic compound because one carbon atom is $\mathrm{sp}^{3}$ hybridized so it also does not follow criteria of aromaticity.

It is a aromatic compound because it follow Huckel's rule and having $(4 n+2) \pi$ electrons where, $\mathrm{n}=0,1,2,3, \ldots \ldots$
3 Cycloheptatriene
4 Cycloheptatrienyl cation
Explanation:
For an aromatic compound it must have cyclic structure, with planer structure i.e. compound having $\mathrm{sp}^{2}$ hybridized carbon and it must be follow (4n $+2) \pi$ electron system where $n=0,1,2,3, \ldots$.
(a.) Cyclopentadienyl cation

It is not a aromatic compound because it has $4 \pi$ electron and does not follow Huckel's rule.
(b.) Cyclo-octatetra-ene

It is also an anti-aromatic compound because it does follow Huckel's rule is $(4 n+2) \pi e^{-}$.

It is an aromatic compound because one carbon atom is $\mathrm{sp}^{3}$ hybridized so it also does not follow criteria of aromaticity.

It is a aromatic compound because it follow Huckel's rule and having $(4 n+2) \pi$ electrons where, $\mathrm{n}=0,1,2,3, \ldots \ldots$