For the Equilibrium PCl₅(g) $\rightleftharpoons$ PCl₃(g) + Cl₂(g), K_c = 2

For the equilibrium PCl₅(g) $\rightleftharpoons$ PCl₃(g) + Cl₂(g) , K_c = 2.0 × 10¹ at 240°C. If pure PCl₅ is placed in a 1.00-L container and allowed to come to equilibrium, and the equilibrium concentration of PCl₃(g) is 0.50 M, what is the equilibrium concentration of PCl₅(g) ?

A) 1 M
B) 0.25 M
C) 0.025 M
D) 0.012 M
E) 6.3 M