For reversible reactions involving gases, the relationship between the equilibrium constants in terms of concentration \( K_C \) and pressure \( K_P \) is given by:
\[
K_P = K_C \times (RT)^{\Delta n_g}
\]
where \( \Delta n_g \) is the change in the number of moles of gas between products and reactants.
This is derived from the ideal gas law.
In the given options, \( K_P \) is correctly related to \( P^{\Delta n_g} \) in option (b), which is a simplified form of the correct relationship.
Thus, the correct answer is (b).