Which process results in the breakdown of unstable nuclei into smaller nuclei?

The process that results in the breakdown of unstable nuclei into smaller nuclei is known as radioactive decay. During radioactive decay, an unstable atomic nucleus loses energy by emitting radiation. This decay can result in the transformation of the unstable nucleus into a different element or a more stable isotope, often leading to smaller nuclei being formed in the process.

Radioactive decay is a natural process that occurs without any external influence and can involve various forms of radiation, including alpha particles, beta particles, or gamma rays, depending on the type of decay. In contrast, nuclear fission involves splitting a heavy nucleus into smaller nuclei, but this process typically requires an external trigger, such as the absorption of a neutron. Nuclear fusion is the process of combining light nuclei to form a heavier nucleus, which also differs fundamentally from the breakdown of nuclei. Chemical reactions, on the other hand, involve the rearrangement of electrons in atoms and do not result in the alteration of the nuclear structure. Therefore, the answer is clearly rooted in the concept of instability in atomic nuclei leading to their natural breakdown and the formation of more stable configurations.