Calculate the percentage purity of H₂O₂ in a 0.200 g impure sample whose 20.0 mL solution reacts completely with 0.316 g of KMnO₄ in an acidic medium.

Given: Molar mass of H₂O₂ = 34 g mol⁻¹; molar mass of KMnO₄ = 158 g mol⁻¹.

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