Why can't we use Concentrated H2SO4 for drying ammonia?
Since NH3 is a base and H2SO4 is an acid, together they will form a salt.
Since NH3 is base and concentrated H2SO4 is an acid, the latter cannot dry the gas. Instead, the acid will react with ammonia to form white fumes of (NH4)2SO4.
2NH3+Conc.H2SO4→(NH4)2SO4