A 350-Mol Sample of HI Is Placed in a 1 $\rightleftharpoons$

A 3.50-mol sample of HI is placed in a 1.00-L vessel at 460°C, and the reaction system is allowed to come to equilibrium. The HI partially decomposes, forming 0.266 mol H₂ and 0.266 mol I₂ at equilibrium. What is the equilibrium constant K_c for the following reaction at 460°C?
½ H₂(g) + ½ I₂(g) $\rightleftharpoons$ HI(g)

A) 1.23 × 10²
B) 8.10 × 10^-3
C) 2.40 × 10^-2
D) 11.1
E) 6.45