which model represents the process of nuclear fusion?

Brief Explanations:

Nuclear fusion is the process where two or more atomic - nuclei combine to form a single, heavier nucleus. The bottom - left model shows smaller nuclei coming together to form a larger nucleus, which is characteristic of nuclear fusion. The other models represent nuclear fission (top - right, where a large nucleus splits into smaller ones) or other nuclear processes.

Answer:

The bottom - left model.