For the reaction, 2NO₂(g) ⇌ N₂O₄(g), when S = 176.0 J/K and H = 57.8 kJ/mol, the magnitude of ΔG° at 298 K for the reaction is __________ₖJ/mol. (Nearest integer)
a. -10
b. -20
c. 20
d. 10