Show that the role of cone, sulphuric acid is not a dehydrating agent, but used for production of nitronium cation. 

Explanation

Nitration mixture is a mixture of conc. nitric acid and conc. sulphuric acid. Sulphuric acid acts as an acid and donates a proton to nitric acid. The protonated nitric acid, gives nitronium cation by the loss of water molecule.
`HHSO_(4)+HNO_(3) to HSO_(4)^(-)+H_(2)O^(+) -NO_(2) , H_(2) overset(+)(O) NO_(2) to NO_(2)^(+)+ H_(2)O`
Benzene gives nitorbenzene by electrophilic substitution.
`C_(6)H_(6)+NO_(2)^(+) to C_(6)H_(5)NO_(2)+H^(+) , H^(+)+HSO_(4)^(-) to H_(2)SO_(4)`