Which compound amongst the following is not an aromatic compound?
(1)

An aromatic compound must be cyclic, planar, fully conjugated, and follow Huckel's rule ($4n+2$ $\pi$ electrons).Option D (typically cyclooctatetraene or a specific non-planar ring provided in the paper) is not aromatic. Cyclooctatetraene ($8$ $\pi$ electrons) is non-planar (tub-shaped) to avoid anti-aromaticity, hence it is non-aromatic.