Which of the following compounds after mixing can produce blue colouration? (I) K4[Fe(CN)6] and FeCl3 solution (II) NH4OH and CuSO4 solution (III) Adding anhydrous CuSO4 to water (IV) NH4OH + NiSO4 so

Question

Which of the following compounds after mixing can produce blue colouration? (I) K4[Fe(CN)6] and FeCl3 solution (II) NH4OH and CuSO4 solution (III) Adding anhydrous CuSO4 to water (IV) NH4OH + NiSO4 solution Choose the correct code:

Prashant Kotian · Accepted Answer

Correct answer: D. Step 1: In the first reaction, Cu2+ oxidizes I- to triiodide ions (I3-) in the presence of excess iodide, while being reduced to Cu+ which precipitates as copper(I) iodide: 2Cu2+ + 5I- -> 2CuI↓ + I3-. Thus, [X] is I3-. Step 2: Triiodide (or iodine in KI) is titrated with sodium thiosulfate (S2O32-), which reduces it back to iodide (I-): I3- + 2S2O32- -> 3I- + S4O62-. Thus, [Y] is I-. Step 3: This identifies X as I3- and Y as I-, matching option (a).

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