Answer: 2 - The nucleus of an atom is split apart
Explanation: Any reaction involving the nucleus of an atom is called a nuclear reaction. It is different from ordinary chemical reactions that involve electrons because it involves the release of large amount of energy. Nuclear reactions can be classified as nuclear fission and nuclear fusion.
A nuclear reaction in which a nucleus of an atom is split into two smaller atoms with a release of large amount of energy is called nuclear fission. A nuclear reaction that involves the combination of lighter nuclei of elements to form heavier atoms that are more stable with the release of a large quantity of energy is called nuclear fusion.
