What is a fundamental difference between nuclear fission and fusion?

A fundamental difference between nuclear fission and fusion lies in their processes. Fission involves the splitting of the nucleus of a heavy element, such as uranium or plutonium, into two or more smaller nuclei, along with the release of a significant amount of energy. This process is commonly utilized in nuclear reactors to produce electricity.

In contrast, fusion is the process where two light atomic nuclei, such as those of hydrogen, combine to form a heavier nucleus, also releasing energy in the process. Fusion is the reaction that powers stars, including our Sun, as it occurs under extreme temperatures and pressures that allow the nuclei to overcome their electrostatic repulsion.

The other options may seem appealing, but they don't accurately distinguish between fission and fusion. For example, the energy output of fission and fusion is not equal, and while fusion is often discussed in terms of its potential for energy generation, fission is currently the predominant method used in power plants. Additionally, fusion does occur in stars, which are essentially massive reactors where the temperatures and pressures facilitate this process.