In which of the following reactions NH3 gas evolution occurs? — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Identify the state of the starting materials. Lead(II) sulfide (PbS↓) is an insoluble black precipitate. Step 2: Analyze the reaction with dilute nitric acid. Dilute HNO3 acts as an oxidizing agent, oxidizing the sulfide ion (S^2-) to elemental sulfur (S) while being reduced to NO gas, which dissolves the lead sulfide into soluble lead(II) nitrate. Step 3: Since the insoluble lead sulfide precipitate is dissolved and converted into soluble lead nitrate, this is classified as a precipitate dissolution reaction (type B). Thus, the correct option is (b).