Decomposition of $H_2O_2$ follows a first order reaction. In fifty minutes the concentration of $H_2O_2$ decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of $H_2O_2$ reaches 0.05 M, the rate of formation of $O_2$ will be: ($2H_2O_2 \to 2H_2O + O_2$)