For the following reaction in gaseous phase $CO+\large\frac{1}{2}$$O_2 \rightleftharpoons CO_2$ and $\large\frac{K_c}{K_p}$ is

Question

$\begin{array}{1 1} (a)\;(RT)^{1/2} \\(b)\;(RT)^{-1/2}\\ (c)\;RT \\ (d)\;(RT)^{-1} \end{array} $