Why is benzene a resonance structure

Once again, we have our carbon double bonded to an oxygen up here.That's why benzene is carcinogenic.And also have one hydrogen atom.Benzene is a unique molecule when it comes to resonance structures.It is good to think in the terms of molecular orbital theory.

Each carbon atom is also bonded to one hydrogen atom.Benzene is stable due to the resonance that it shows.Benzene shows resonance as it has more than one way to place double bonds in the ring.There are two equivalent resonance structures benzene (c6h6).Notice how the positions of the double bonds differ between the two molecules.commons.wikimedia.org.

However, if benzene existed in two resonance forms with alternating double bonds, we'd have two types of bonds;The six carbon atoms form a ring structure;The three resonance structures which contain positively charged carbons show this fact.These 6 protons are equivalent because they have the same electronic environment.The pyridine has three resonance structures.