What happens to the nucleus of an atom during radioactive decay?

The correct answer is C: It emits radiation and changes its composition.

The correct answer is C: It emits radiation and changes its composition. This supports the learning objective "Define radioactive decay as the process in which an unstable nucleus emits radiation." in Radioactive decay and nuclear radiation because it uses the correct atomic and nuclear radiation relationship for Atoms and nuclear radiation. The other options are less suitable because they do not match the required Radioactive decay and nuclear radiation idea: It gains protons and neutrons; It loses protons and neutrons; It remains unchanged.