In order to get a reaction started the reactants of this type of reaction require the greatest amount of energy:

a. fusion

b. fission

c. physical

d. chemical

The answer is A. Fusion is a reaction type that in order to initiate the reaction a greatest amount of energy should be inputted. This reaction involves two or more atomic nuclei coming very close to each other then colliding and eventually joining to form a new nucleus. The energy needed to do this is very large.