The blue colour in an oxidising flame of a microcosmic bead containing Cu2+ is due to: — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: Nessler's reagent is an alkaline solution of potassium tetraiodomercurate(II), [HgI4]2- in KOH, which specifically detects ammonia gas by forming a brown precipitate called the iodide of Millon's base. Step 2: Boiling ammonium chloride (NH4Cl) with sodium hydroxide (NaOH) releases ammonia gas (NH3): NH4Cl + NaOH -> NaCl + NH3↑ + H2O. Step 3: Passing this ammonia gas through Nessler's reagent yields the brown iodide of Millon's base precipitate. Thus, option (b) is correct.