NEET 2022, Chemistry Q15: Important Concepts Of Chemical Bonding

Aromaticity requires a planar cyclic system with continuous overlap of $p$-orbitals and $(4n+2)$ $\pi$ electrons (Huckel's rule).

Option (1): cycloheptatrienyl cation (tropylium), 6 $\pi$ electrons, aromatic.

Option (2): cyclopropenyl cation, 2 $\pi$ electrons ($n=0$), aromatic.

Option (3): cycloheptatriene contains an sp${}^3$ CH${}_2$ group, which interrupts the cyclic conjugation. It is non-aromatic.

Option (4): cyclopentadienyl anion, 6 $\pi$ electrons, aromatic.