Solution:

Any physical or chemical change (such as extreme heating, freezing, action of strong electric and magnetic fields, chemical treatment, oxidation, and so on) has no effect on the pace of decay or the nature of the radiation emitted by the substance. This clearly demonstrates that radioactivity is not caused by orbital electrons, which are easily impacted by such changes. As a result, radioactivity must be a property of the nucleus. As a result, radioactivity is a nuclear event.