Radioactivity is defined as unstable nuclei naturally releasing energy by means of decay. Which term describes this phenomenon?

• A. Radioactivity
• B. Radiation
• C. Radioisotope
• D. Half-life

Answer: (A)

The main idea here is the name of the process by which unstable nuclei release energy as they decay. That phenomenon is called radioactivity. Radiation refers to the energy or particles emitted during decay, not the process itself. A radioisotope is a specific unstable nuclide that undergoes radioactive decay. Half-life is the time it takes for half of a radioactive sample to decay, a rate-related property, not the process name. So radioactivity best describes the observed phenomenon.