Question

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

Answer 1

C. the concentration the products and reactants is constant.

Answer 2

Answer is: C. the concentration the products and reactants is constant.

In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time.  

Reaction rates of the forward and backward reactions are equal and  there are no changes in the concentrations of the reactants and products.