(i) Radioactivity : It is a nuclear phenomenon. It is the process of spontaneous emission of α or β and γ radiations from the nuclei of atoms during their decay.
(ii) Nuclear Waste : The radioactive material after its use is known as nuclear waste.
(iii) The nuclear waste obtained from laboratories, hospitals etc. must be first kept in thick casks and then they must be buried in the specially constructed deep underground stores.