What is the main product in the reaction between benzene (C₆H₆) and oleum followed by reaction with sodium hydroxide (NaOH) and a proton (H⁺)?

Phenol

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.

C₆H₆ + oleum ---> C₆H₅-SO₃H + NaOH/H⁺   -----> C₆H₅OH