Question: when nh4cl is added to a solution of nh4oh?
Answer: NH4Cl is strong electrolyte, it decomposes completely. While the NH4OH is weak base it does not ionises completely. Thus due to presence of common ion NH4+ in NH4Cl, it supresses the ionisation of weak base NH4OH in order to decrease the OH-concentration so that higher group cations will not get precipitated.