Dear Student,
Ammonia is basic in nature while ammonium chloride is acidic because NH4Cl (Ammonium chloride) is a salt of strong acid and weak base. Cl- being a weak base will not hydrolyze in water. So when NH4Cl will dissolve in water following equilibrium takes place:
NH​​​​​4+ + H2O <————> NH4OH + H+
The solution is acidic because of presence of H+ ions in solution.
Regards