At dynamic equilibrium:

Dynamic equilibrium occurs in a closed system when a reversible chemical reaction proceeds at the same rate in both directions. 1. **Reversibility:** A reaction like $A + B \rightleftharpoons C + D$ can go forward (forming products) and backward (reforming reactants). 2. **The 'Dynamic' Nature:** Unlike a static system, the reactions do not stop. They continue to occur at the molecular level. 3. **Rate Equality:** Equilibrium is reached when the speed of the forward reaction ($r_f$) is exactly equal to the speed of the reverse reaction ($r_r$). Mathematically: $$r_f = r_r$$ 4. **Concentrations:** Because the rates are equal, the amount of reactants and products being consumed and produced cancels out. Therefore, their concentrations remain constant over time, although they are rarely equal to each other. Thus, the correct choice is that the forward rate equals the reverse rate.