Answer:
The expression for an equilibrium constant for the given reaction:
![K_c=([H_2O]^2)/([H_2]^2[O_2)}](https://img.qammunity.org/2019/formulas/chemistry/college/te6pjg6wivnj1apxz4n8zpdgdkyus8xy9h.png)
Step-by-step explanation:
Equilibrium constant is defined as the ratio of concentration of products to the concentration of reactants each raised to the power their stoichiometric ratios. It is expressed as

K is the constant of a certain reaction when it is in equilibrium, while Q is the quotient of activities of products and reactants at any stage other than equilibrium of a reaction.
For the given chemical reaction:

The expression for an equilibrium constant will be given by:
![K_c=([H_2O]^2)/([H_2]^2[O_2)}](https://img.qammunity.org/2019/formulas/chemistry/college/te6pjg6wivnj1apxz4n8zpdgdkyus8xy9h.png)