We are being asked to calculate K_p for the decomposition of phosgene (CoCl₂) where its K_c is given.

COCl_2(g) ⇌ CO_(g) + Cl_2(g)

When dealing with equilibrium:

• K_c → equilibrium units are in molarity 
• K_p → equilibrium units in terms of pressure

Kp and Kc are related to one another by the following equation below: 

$\boxed{{\mathbf{K}}_{\mathbf{p}}\mathbf{=}{\mathbf{K}}_{\mathbf{c}}{\left(\mathbf{RT}\right)}^{\mathbf{∆}\mathbf{n}}}$