What defines an aromatic hydrocarbon?

An aromatic hydrocarbon is defined by the presence of a ring structure that exhibits resonance and has delocalized pi electrons, akin to benzene. This unique structure endows aromatic hydrocarbons with distinctive stability and chemical properties, often referred to as aromaticity. The ring must typically consist of six carbon atoms in a planar arrangement, allowing the pi electrons to circulate, which contributes to the overall stabilization of the molecule. This characteristic is crucial in distinguishing aromatic compounds from other types of hydrocarbons, as it suggests a specific type of bonding and reactivity that is not found in aliphatic hydrocarbons, which may be straight-chain or branched structures without such resonance stabilization. The other options do not encompass the essential features of aromatic hydrocarbons, which are fundamentally tied to their ring structure and the phenomenon of aromaticity.