Group reagent: NH4Cl → NH4+ + Cl– ; NH4OH ⇌ NH4+ + OH–
H2S ⇌ 2H+ + S2- ; H+ + OH– → H2O
Radicals: Zn2+, Mn2+
Here, NH4Cl is a strong electrolyte undergoes complete dissociation, where as NH4OH– and H2S are weak electrolytes undergoes partial dissociation and attains equilibrium between their ions and molecules. Along with common ion (NH4+) effect, the H+ and OH- ion combines to form water molecules.
At the same time the metals forms their respective sulphides [ZnS, MnS] Whose solubility product is less than ionic product. Hence, forms precipitate.