Which of the following substances on being heated will give a gas that turns limewater milky? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: In Group III qualitative analysis, the group reagent consists of NH4OH in the presence of NH4Cl. Step 2: Ammonium chloride (NH4Cl) suppresses the dissociation of the weak base NH4OH via the common ion effect of NH4+, reducing the concentration of OH- ions so that only the less soluble Group III hydroxides precipitate, while the more soluble Group IV hydroxides (Ni2+, Co2+, Zn2+, Mn2+) remain in solution. Step 3: Therefore, treating the solution with excess NH4Cl prevents the unwanted co-precipitation of Group IV cations, matching option (b).