The statement "NH4Cl can be prepared by (NH4)2SO4 in group III" is false.
NH4Cl is used alongwith NH4OH in group III. Ammonium chloride provides common ion (ammonium ion) and decreases ionisation of NH4OH. (NH4)2SO4 also provides NH4+ion but it can't be used as SO2−4 ion will precipitate Zn2+,Ca2+,Ba2+andSr2+ ions as their sulphate.