If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?
a. additional substrate will be formed.
b. the reaction will change from endergonic to exergonic.
c. the free energy of the system will change.
d. nothing; the reaction will stay at equilibrium.

d. Nothing; the reaction will stay at equilibrium is the correct answer.

Explanation:

If an enzyme is added to a solution where its substrate and product are in equilibrium, the reaction will stay at equilibrium it will not affect the equilibrium point because there is no change in the free energy and equilibrium constant both stay the same.

When Enzyme is added to a solution where the substrate and product are in equilibrium it may decrease the activation energy but the enzyme will not change the equilibrium as they cannot alter the overall energy production.