Answer: The expression for 
 is written below.
Step-by-step explanation:
Equilibrium constant in terms of partial pressure is defined as the ratio of partial pressures of the products and the reactants each raised to the power their stoichiometric ratios. It is expressed as 

For a general chemical reaction:

The expression for 
 is written as:

The partial pressure for solids and liquids are taken as 1.
For the given chemical equation:

The expression for 
 for the following equation is:

The partial pressure of 
 will be 1 because it is solid.
So, the expression for 
 now becomes:

Hence, the expression for 
 is written above.