The equilibrium constant for the reaction \( \mathrm{A(s)} \rightleftharpoons \mathrm{M(s)} + \tfrac{1}{2} \mathrm{O_2(g)} \) is \( K_p = 4 \). At equilibrium, the partial pressure of \( \mathrm{O_2} \) is ________ \( \text{atm} \). (Round off to the Nearest Integer).
