Final answer:
When nuclear fusion occurs, energy is always released as light nuclei combine to form a heavier nucleus, with some mass converted into energy.
Step-by-step explanation:
The question focuses on the outcomes of nuclear fusion. The statement that is always true when nuclear fusion occurs is that energy is released. During fusion, light nuclei combine to form a heavier nucleus, and this process yields a significant amount of energy due to the conversion of some mass into energy, as per Einstein's equation E = mc². Unlike nuclear fission, which involves splitting heavy nuclei apart, fusion involves merging smaller nuclei. Formation of a new element and the release of neutrons can happen but are not guaranteed. Radioactive decay is not a part of the fusion process itself but may occur separately as unstable nuclei seek stability.