What process occurs when atomic nuclei split apart, releasing a significant amount of energy?

The process that occurs when atomic nuclei split apart, releasing a significant amount of energy, is nuclear fission. During nuclear fission, the nucleus of a heavy atom, such as uranium-235 or plutonium-239, is split into two or more smaller nuclei, along with a few neutrons and a considerable amount of energy. This energy is released as a result of the conversion of mass into energy, in accordance with Einstein's equation, E=mc².

Nuclear fission is the principle behind both nuclear reactors and atomic bombs, as it can produce large amounts of energy from relatively small amounts of fuel. This distinguishes it from other processes such as nuclear fusion, where smaller nuclei combine to form a larger nucleus, or radioactive decay, which involves the transformation of an unstable atom into a more stable one with the emission of radiation. Chemical reactions, on the other hand, involve the rearrangement of electrons around atoms but do not involve changes in the nuclei of atoms. Thus, in the context of splitting atomic nuclei and the associated energy release, nuclear fission is the correct and relevant process.