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How many of the following reagent combinations produce a pink-colored solution, precipitate, or product? (i) MnCl2 + H2S(g) + HCl (ii) Mn2+ + S2O8²- (persulfate) (iii) Mn2+ + NaBiO3 + HNO3 (iv) Mn2+ + PbO2 + HNO3 (v) K2MnO4 + Cl2 (vi) ZnCl2 + H2S + NH4OH(aq)

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

(i) MnCl2 + H2S in acidic (HCl) medium: in acidic conditions MnS does NOT precipitate (Ksp too large for acidic medium). No pink. (ii) Mn2+ + S2O8²-: persulfate oxidizes Mn2+ to MnO4- (purple/permanganate), which could be considered purple-pink. This gives pink/purple color. (iii) Mn2+ + NaBiO3 + HNO3: NaBiO3 is a strong oxidizer that converts Mn2+ to MnO4- (permanganate, purple-pink). PINK. (iv) Mn2+ + PbO2 + HNO3: PbO2 also oxidizes Mn2+ to MnO4-. PINK/purple. (v) K2MnO4 + Cl2: Cl2 oxidizes MnO4²- (green) to MnO4- (purple-pink). Could be counted as pink. (vi) ZnCl2 + H2S + NH4OH: gives white ZnS precipitate. NOT pink. So pink/purple: (ii), (iii), (iv), (v) = 4 combinations. But (i) and (vi) are not pink. Count = 4. Answer: 4.

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