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

Option (B) is the correct answer.

Explanation:

Activation energy is the minimum amount of energy necessary for the reactant molecules to start a chemical reaction.

So, reactant molecules must reach the activated complex before a chemical reaction and once the activated complex is crossed by the reactants then it leads to formation of products easily.

Hence, we can conclude that the activation energy must be reached before a chemical reaction can begin.