For the reaction,  $\mathrm{CO}\left(g\right)+{\mathrm{Cl}}_2\left(g\right)\rightleftharpoons {\mathrm{COCl}}_2\left(g\right)$ then $K_p/K_c$ is equal to :

$\mathrm{CO}\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\iff {\mathrm{COCl}}_2\left(\mathrm{g}\right)$

In given equation 

$\mathrm{\Delta n}=1-(1+1)=-1$

Relation between ${\mathrm{K}}_{\mathrm{p}}$and ${\mathrm{K}}_{\mathrm{c}}$is

${\mathrm{K}}_{\mathrm{p}}={\mathrm{K}}_{\mathrm{c}}(\mathrm{RT}{)}^{\mathrm{\Delta n}}$

${\mathrm{K}}_{\mathrm{p}}/{\mathrm{K}}_{\mathrm{c}}=(\mathrm{RT}{)}^{-1}$

$=1/\left(\mathrm{RT}\right)$

$=\frac{1}{\mathrm{RT}}$