A 20.0 mL solution containing 0.2 g impure H_2 O_2 reacts completely with 0.316 g of KMnO_4 in acid solution. The purity of H_2 O_2 (in %) is \ \ \ \…

A $\displaystyle 20.0$ mL solution containing $\displaystyle 0.2$ g impure $\displaystyle \mathrm{H}_2 \mathrm{O}_2$ reacts completely with $\displaystyle 0.316$ g of $\displaystyle \mathrm{KMnO}_4$ in acid solution. The purity of $\displaystyle \mathrm{H}_2 \mathrm{O}_2$ (in %) is \_\_\_\_ (mol. wt. of $\displaystyle \mathrm{H}_2 \mathrm{O}_2=34$; mol. wt. of $\displaystyle \mathrm{KMnO}_4=158$ )