Question

what is true when a reaction has reached equilibrium?
o the reaction has stopped.
o the concentration of the reactants is changing.
o the concentration of the products is changing.
o the concentration of products and reactants is constant.

Explanation:

At equilibrium, the forward and reverse reaction rates are equal. This means that while the reactions are still occurring (so the reaction has not stopped), the concentrations of reactants and products remain constant because the rate at which reactants are being converted to products is the same as the rate at which products are being converted back to reactants. If the concentration of reactants or products were changing, the system would not be at equilibrium.

Answer:

The concentration of products and reactants is constant.