What is the expression for the equilibrium constant, Kc, for the following heterogeneous reaction?

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What is the expression for the equilibrium constant, Kc, for the following heterogeneous reaction? 4 H3O+(aq) + 2Cl-(aq) + MnO2(s) <—> Mn2+(aq) + 6H2O(l) + Cl2(g)