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A 100 mL solution of 0.4 M acidified KMnO4 can be completely decolorised by which of the following?
- 200 mL of 1 N K2Cr2O7 solution
- 300 mL of 0.5 M H2O2 solution
- 100 mL of 0.8 N KI solution
- 75 mL of 1.4 N H2C2O4 solution
Correct answer: 200 mL of 1 N K2Cr2O7 solution
Solution
KMnO4 in acid has n-factor 5, so its normality = 2 N and meq = 200. Option A: 1 N × 200 mL = 200 meq — exact match. Option B: H2O2 (n=2, acting as reducer: H2O2 → O2) gives 0.5×2×300 = 300 meq (excess). Option C: KI (n=1) gives 0.8×100 = 80 meq (insufficient). Option D: H2C2O4 (n=2) gives 1.4×75 = 105 meq (insufficient).
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