The low of mass action applicable to heterogenous equilibria.

Explanation

### Step-by-Step Solution:

1. **Understanding the Law of Mass Action**: The law of mass action states that the rate of a chemical reaction is proportional to the product of the active masses (or concentrations) of the reactants, each raised to the power of their respective coefficients in the balanced chemical equation.

2. **Application to Heterogeneous Equilibria**: Heterogeneous equilibria involve reactants and products in different phases (e.g., solid, liquid, gas). The law of mass action can still be applied to these systems, but it is important to note that only the concentrations (or partial pressures) of the gaseous and aqueous species are included in the equilibrium expression. The concentrations of pure solids and pure liquids are not included because their activities are defined to be 1.

3. **Formulating the Equilibrium Expression**: For a general heterogeneous reaction:
\[
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