Which one of the following is aromatic? (A) Cyclopentadienyl cation (B) Cyclooctatetraene (C) Cycloheptatriene (D) Cycloheptatrienyl cation

Among the options provided, the compound that is aromatic is (A) Cyclopentadienyl cation.

Aromaticity refers to a property of cyclic, planar compounds that possess a specific pattern of alternating single and double bonds, known as a conjugated system, and fulfill the following criteria:

The molecule must be cyclic.
It must be planar or nearly planar.
It must possess a continuous loop of overlapping p-orbitals.
It must have a total of (4n + 2) π electrons, where "n" is a non-negative integer.
The Cyclopentadienyl cation (C₅H₅⁺) satisfies all these criteria. It has a cyclic structure, is planar, possesses a continuous loop of overlapping p-orbitals, and has 6 π electrons [(4n + 2) with n = 1]. Therefore, the Cyclopentadienyl cation is considered aromatic.