Consider the nitration of benzene using mixture of conc.H2SO4 and HNO3. If a large amount of KHSO4 is added to the mixture, the rate of nitration will be

Mechanism of nitration is : HNO3+2H2SO4⟶NO2++2HSO4-+H3O+If a large amount of  KHSO4 is added then conc. of HSO4- ions increases and the reaction will be shifted in backward direction hence, the rate of nitration will be slower.