Provide basic information about aromatic hydrocarbons. Explain and give examples of the following: $(i)$ Aromatic compounds $(ii)$ Arenes $(iii)$ Benzenoid compounds $(iv)$ Non-benzenoid compounds.

(N/A) Aromatic hydrocarbons are also known as 'arenes'. Since most of them possess a pleasant odour (Greek; aroma meaning pleasant smelling),this class of compounds was named as 'aromatic compounds'.
$(i)$ Aromatic compounds: These are cyclic,planar compounds that follow $H$ückel's rule (possess $(4n+2) \pi$ electrons,where $n = 0, 1, 2, ...$).
$(ii)$ Arenes: These are aromatic hydrocarbons,typically containing at least one benzene ring.
$(iii)$ Benzenoid compounds: These are aromatic compounds that contain at least one benzene ring in their structure. Examples include benzene,toluene,naphthalene,and biphenyl.
$(iv)$ Non-benzenoid compounds: These are aromatic compounds that do not contain a benzene ring in their structure. An example is azulene.