A graduate student places 0.272 mol of PCl₃(g) and 8.56 × 10^-4 mol of PCl₅(g) into a 0.718-L flask at a certain temperature.

PCl₅(g) is known to dissociate as follows:

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

After the reaction attains equilibrium, the student finds that the flask contains 2.51 × 10^-4 mol of Cl₂. Calculate the equilibrium constant K_c for the reaction at this temperature.

a. 0.114

b. 8.51 × 10^2

c. 0.157

d. 8.88 × 10⁴

e. 2.40 × 10⁴