What must happen before a chemical reaction can begin?
a.)the activation energy must be exceeded.
b.)the activation energy must be reached.
c.)the concentrations of products and reactants must be equal.
d.) the concentration of reactant molecules must be reduced.

The answer is B.)The activation energy must be reached. The energy required to break the bonds of reactant molecules. Catalyst work by decreasing the activation energy of a reaction. If the activation energy required for a chemical reaction were reduced, If the activation energy required for a chemical reaction were reduced.