The major product formed when benzene is treated with a mixture of sulfuric and nitric acid in the presence of concentrated sulfuric acid as a catalyst is nitrobenzene. This reaction is known as nitration of benzene.The reaction mechanism occurs in the following steps:1. Formation of nitronium ion NO2+ : Concentrated sulfuric acid protonates nitric acid HNO3 to form nitronium ion NO2+ and bisulfate ion HSO4- .HNO3 + H2SO4 -> NO2+ + HSO4- + H2O2. Electrophilic attack on benzene: The nitronium ion NO2+ acts as an electrophile and attacks the benzene ring, which is rich in electron density due to the delocalized electrons. This attack forms a resonance-stabilized carbocation called the sigma complex or arenium ion.3. Deprotonation: A proton from the sigma complex is removed by the bisulfate ion HSO4- , which acts as a base, to regenerate the aromaticity of the benzene ring. This step forms nitrobenzene as the major product and sulfuric acid.Overall, the reaction can be summarized as:Benzene + HNO3 -> Nitrobenzene + H2OThis nitration reaction is an example of electrophilic aromatic substitution, where the nitro group NO2 substitutes a hydrogen atom on the benzene ring.