A 20.0 mL solution containing 0.2 g impure H₂O₂ reacts completely with 0.316 g of KMnO₄ in acid solution. What is the percentage purity of H₂O₂ ?
[Given: mol. wt. of H₂O₂ = 34 ; mol. wt. of KMnO₄ = 158]

1. 80
2. 85
3. 90
4. 92