Classify the following reaction

Mg(s) + 2 HCl (aq) --> MgCl2 (aq) + H2 (8)

Which best describes the activation energy of a chemical reaction? a. the combined energy of all the reactants b. the amount of energy required for a reaction to occur c. the difference in energy between products and reactants d. the potential energy stored in the bonds of reactants and products