On a typical plot of the Gibbs free-energy change ΔG versus the extent of reaction (reaction progress), which point most accurately represents the equilibrium state of the system?
a) The point where ΔG reaches its most negative value (the minimum on the curve).
b) The point where ΔG equals zero and the curve has a horizontal tangent.
c) The point where ΔG equals the enthalpy change ΔH of the reaction.
d) The point where ΔG attains its greatest positive value (the peak of the curve, representing the energy barrier).