Correct Answer: D
Explanation:
Fission and fusion are alike in that both are energy-releasing nuclear reactions that involve transformation of one or more elements into other elements. However, they differ in important ways: Fission doesn’t require high temperature; fusion does. Fission involves heavy nuclei; fusion involves light nuclei. As the names imply, fission is the splitting apart of a nucleus while fusion is the joining together of nuclei. The concept of critical mass applies to fission, but not fusion.