Show that the role of conc. 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 act as an acid and donates a proton to nitric acid.
`H HSO_(4) +HNO_(3) to HSO_(4)^(-) +H_(2)overset(+)O-NO_(2)`
The protonated nitric acid, gives nitronium cation by the loss of water molecule.
`H_(2)overset(+)ONO_(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^(+)`
Sulphuric acid is obtained back from bisulphate ion.
`H^(+)+HSO_(4)^(-) to H_(2)SO_(4)`