Dinitrogen Tetroxide Partially Decomposes According to the Following Equilibrium

Dinitrogen tetroxide partially decomposes according to the following equilibrium:
N₂O₄(g) → 2NO₂(g)
A 1.000-L flask is charged with 3.00 × 10^-2 mol of N₂O₄.At equilibrium,2.36 × 10^-2 mol of N₂O₄ remains.K_eq for this reaction is ________.

A) 0.723
B) 0.391
C) 0.212
D) 6.94 × 10^-3
E) 1.92 × 10^-4