- At equilibrium, the Gibbs free energy change \( \Delta G \) is equal to zero. This is because, at equilibrium, the system has reached a state where there is no further net change in the composition.
- Therefore, \( \Delta G = 0 \) at equilibrium, indicating that the forward and reverse reactions occur at the same rate.
Conclusion:
The value of Gibbs free energy change at equilibrium is zero, so the correct answer is (D).