Which is the best definition of activation energy?
o the energy required to end a chemical reaction
o the energy required to bind a substrate to an active site
o the energy required to form or break the bonds of reactant molecules
o the energy required to re-form bonds in product molecules

The best definition of activation energy is that it is the energy required to form or break the bonds of reactant molecules.

Option C

Explanation:

The activation energy is the initial energy or the threshold energy in any chemical reaction which is needed to proceed the reaction. Every chemical reaction should pass that hill of activation energy to form the products. So, an activation energy is the threshold energy required by the reactants to increase the rate of reaction.

But the reverse process will require more positive activation energy than the forward process as in case of reverse process, the products will have the lowest energy state compared to the reactants energy state. Thus, the best to define activation energy is the energy required to create or cut the bonds in reactant molecules.