At 298K, pH of a solution containing one mole each of  NH4OH and  NH42SO4  will be ( pKb of NH4OH=4.8)

pOH=pKb+ log VsNsVbNb ; NH4OH is monoacidic base but NH42SO4 is bivalent; pOH=4.8+ log1×21×1;[ considering one  unit volume of salt and base] pOH=4.8+0.301=5.1;    pH=14-5.1=8.9