If the equilibrium constant for the reaction $\mathrm{H}_{2}+$ $\frac{1}{2} \mathrm{O}_{2} \rightleftharpoons \mathrm{H}_{2} \mathrm{O}$ is $K,$ the equilibrium constant for the reaction $2 \mathrm{H}_{2} \mathrm{O} \rightleftharpoons 2 \mathrm{H}_{2}+\mathrm{O}_{2}$ at the same temperature is
$(a) 1 / K$
$(b) 1 /(2 K)$
$(c) 2 K$
$(d) K^{2}$
$(e) 1 / K^{2}$