Dinitrogen Tetroxide Partially Decomposes According to the Following Equilibrium: N₂O₄

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_c for this reaction is ________.

A) 0.723 mol L^-1
B) 0.391 mol L^-1
C) 0.212 mol L^-1
D) 6.94 × 10^-3 mol L^-1
E) 1.92 × 10^-4 mol L^-1