In which condition does dynamic equilibrium exist?

Dynamic equilibrium exists when the forward and reverse reactions occur at the same rate, leading to a condition where the concentrations of reactants and products remain constant over time. In this state, the system is balanced; although reactions are still happening, there is no net change in the concentrations of the substances involved.

This balance is a hallmark of dynamic equilibrium, where the rate at which products are formed is equal to the rate at which they are converted back into reactants. Therefore, even though the individual molecules are still reacting, the overall concentrations do not change.

In contrast, the other conditions suggested do not define a state of dynamic equilibrium. For example, rapidly accumulating products or the complete consumption of reactants would indicate that the reaction is moving toward completion rather than achieving equilibrium. Similarly, having no solute left means the reaction has effectively stopped, not that it is in a state of dynamic balance.