A chemical reaction $$X(g) + Y(g) \rightarrow Z(g)$$ has the following mechanism. 

$$X(g) + S(s)$$ $$\rightleftharpoons$$ [X-S](s)$$ 

$$[X-S](s) + Y(g)$$ $$\rightleftharpoons$$ $$Z(g) + S(s)$$ ; [where (S) is solid catalyst]

 The overall equilibrium constant for the above reaction can be represented as

A

$$K = \frac{k_1 k_2}{k_3 k_4}$$

B

$$K = \frac{k_1 k_3}{k_2 k_4}$$

C

$$K = \frac{k_4 k_1}{k_2 k_3}$$

D

$$K = \frac{k_4 k_2}{k_3 k_1}$$