At a certain temperature, 2.00 moles of phosphorus(V) chloride, PCl5, was placed in a 1.0 L vessel and permitted to react as shown:

Question

PCl5 (g) <-> PCl3 (g) + Cl2(g)

At equilibrium, the container held 0.40 PCl5. What is the numerical value of Kc for the system as written?

A) 10
B) 6.4
C) 2.0
D) 1.2