Step-by-step explanation:
The question requires us to explain why energy is not positioned on the left side of a chemical reaction that represents a nuclear fusion.
By definition, a nuclear fusion is the process in which two (or more) light nuclei collide and produce a heavier nucleus. In this process, energy is not required for the collision between the nuclei happen, but it is released in a great amount when the heavier nucleus is formed.
Because energy is released in the nuclear fusion process, it must be represented on the products side of the reaction.
Final answer: energy cannot be on the left side of a nuclear fusion chemical equation because energy is actually released in the nuclear fusion process, thus it must be represented on the products side (right side).