Final answer:
Nuclear fusion is a process that combines light nuclei to form heavier ones, releasing large amounts of energy, which is the primary source of energy in the sun.
Step-by-step explanation:
The true statement about nuclear fusion is that It occurs in the sun. Nuclear fusion is the process where very light nuclei combine to form heavier nuclei, releasing a significant amount of energy in the process. This fusion of hydrogen into helium is the primary source of energy in the sun and other stars. Unlike nuclear fission, which involves the splitting of heavy atoms, nuclear fusion requires the fusing of light elements such as hydrogen. Despite the potential for controlled fusion as a power source, current technology has not yet mastered this process to the point where it can be controlled easily on Earth.