Final answer:
Nuclear fusion and nuclear fission convert some mass into energy.
Step-by-step explanation:
Both nuclear fusion and nuclear fission convert some mass into energy. In nuclear fusion, the nuclei of lighter atoms combine to form a heavier nucleus, releasing a tremendous amount of energy in the process. Nuclear fission, on the other hand, involves the splitting of a heavy nucleus into lighter nuclei, also releasing a significant amount of energy. Both processes are accompanied by a conversion of mass into energy according to Einstein's famous equation, E = mc^2.
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