The Standard Free Energy Change Associated with the Dissolution of Ammonium

Multiple Choice

The standard free energy change associated with the dissolution of ammonium nitrate in water is -6.73 kJ/mol at 298.15 K. NH₄NO₃(s) $\leftrightharpoons$ NH₄NO₃(aq)
Which of the following is the equilibrium constant for the reaction? (R = 8.314 J/K?mol)

A) 1.9 × 10^-3
B) 6.6 × 10^-2
C) 1.0
D) 15
E) 5.2 × 10²