17. At a certain temperature, K for the reaction :  2NO2⇌ N2O4  is 7.5 L/mol. If 2.0 mol of NO2 is placed in a 2.0-liter container and permitted to react at this temperature,calculate the concentration of N2O4 at equilibrium.
(A) 0.39 mol/L;
(B) 0.65 mol/L;
(C) 0.82 mol/L;
(D) 7.5 mol/L;
(E) none of these