Final answer:
As the reaction proceeds towards equilibrium, ΔG becomes less negative and ΔG° stays the same.
Step-by-step explanation:
As the reaction proceeds towards equilibrium, the concentrations of reactants and products change. In this case, [Y] decreases while [X] increases. Initially, ΔG is a large negative number, indicating that the reaction is spontaneous and favors the formation of products. However, as the reaction progresses towards equilibrium, ΔG becomes less negative. The value of ΔG°, which represents the standard free energy change, remains the same throughout the reaction. Therefore, the correct choice is (a) ΔG becomes less negative and ΔG° stays the same.