Benzene is a chemical compound made of a ring of six carbon atoms each attached to a hydrogen atom (C6H6). This "benzene ring" is a key structure of many organic compounds. It occurs naturally in crude oil. It is colorless and highly flammable. It is a common component of gasoline and is used extensively in the chemical industry as a precursor.

Although once sold on a retail level as a degreasing solvent and for other applications, it's use has been restricted to industrial applications since the 1970s since it was shown to be a carcinogen and was highly toxic to bone marrow. It is also a significant environmental pollutant due to its wide use in industry prior to 1970. 

Benzene at Wikipedia

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