Dinitrogen Tetroxide Partially Decomposes According to the Following Equilibrium $\mathrm { N } _ { 2 }$

Dinitrogen tetroxide partially decomposes according to the following equilibrium: $\mathrm { N } _ { 2 }$ $\mathrm { O } _ { 4 }$ (g) ? $2 \mathrm { NO } _ { 2 }$ (g) A 1.000 L flask is charged with 6.00 × 10^-2 mol of $\mathrm { N } _ { 2 }$ $\mathrm { O } _ { 4 }$ .At equilibrium,3.21 × 10^-2 mol of $\mathrm { N } _ { 2 }$ $\mathrm { O } _ { 4 }$ remains. $K _ { c }$ for this reaction is ________.

A) 10.3 mol L^-1
B) 1.74 mol L^-1
C) 0.465 mol L^-1
D) 2.42 × 10^-2 mol L^-1
E) 9.70 × 10^-2 mol L^-1