The correct answer is A.) A change in the structure of the nucleus.
Explanation:
A nuclear change differs from a chemical or physical change because, during this, the structure of the nucleus changes, and this leads to a change in the element, which does not occur in chemical changes that only involve electrons or in physical changes that only affect the form of substances. Moreover, nuclear changes can occur through processes such as fission that implies the nucleus dividing or fusion, in which different nuclei combine. According to this, a nuclear change involves "a change in the structure of the nucleus".
