Which of the following is a fused cyclic aromatic compound?

A fused cyclic aromatic compound is an aromatic hydrocarbon in which two or more benzene rings share common carbon atoms, resulting in a continuous ring system. Among the given options, naphthalene is the compound that fits this definition. Naphthalene consists of two fused benzene rings, sharing two adjacent carbon atoms. Its molecular formula is C₁₀H₈.

Naphthalene is the simplest example of a polynuclear aromatic hydrocarbon (PAH). It exhibits complete aromatic character because both rings share delocalized π-electrons, providing extra stability to the structure. Each carbon atom in naphthalene is sp² hybridized, and the molecule is completely planar, allowing maximum delocalization of electrons across both rings.

The compound is a white crystalline solid with a characteristic mothball odor. It is commonly used in moth repellents, dyes, and as a starting material in the synthesis of other organic compounds like phthalic anhydride. Naphthalene is obtained mainly from the distillation of coal tar and also forms during the incomplete combustion of organic materials.

Other options such as diphenylamine, diphenylmethane, and biphenyl consist of two benzene rings but are not fused; instead, the rings are connected by a single bond or a bridging group. Because they do not share carbon atoms, they are not considered fused cyclic systems.

Understanding fused aromatic systems is important in organic chemistry because these structures exhibit unique electronic, optical, and chemical properties. Compounds like anthracene and phenanthrene are larger members of this fused aromatic family. Naphthalene serves as the simplest model compound to study the behavior of polycyclic aromatic hydrocarbons in reactions and environmental processes