Which type of energy is released through nuclear fission or fusion?

Nuclear energy is released specifically through the processes of nuclear fission and fusion. In nuclear fission, the nucleus of a heavy atom splits into lighter nuclei, releasing a significant amount of energy due to the strong nuclear forces that hold the nucleus together. In fusion, lighter atomic nuclei combine under extreme temperatures and pressures to form a heavier nucleus, which also results in a release of energy. The energy released in both processes is a consequence of changes in the binding energy of the nuclei involved, making it a form of nuclear energy.

Thermal energy, while often a byproduct of fission and fusion, is not the energy type released during the nuclear reactions themselves. Chemical energy pertains to bond interactions within atoms and molecules, and potential energy usually refers to energy stored due to position. Hence, nuclear energy is the most accurate classification for the energy released in these nuclear reactions.