Which term denotes the breakdown of the nucleus that is the origin of radioactivity?

• A. Radioactivity
• B. Nuclear decay
• C. Half-reactions
• D. Cell Potential

Answer: (B)

The key idea is the transformation process by which unstable nuclei convert into more stable forms. This spontaneous change is what we observe as radioactivity, and it occurs through nuclear decay—emitting particles or radiation such as alpha particles, beta particles, or gamma rays as the nucleus moves toward greater stability. Radioactivity describes the phenomenon itself, while nuclear decay names the actual mechanism behind it. The other terms don’t fit: half-reactions are about electron transfer in redox chemistry, and cell potential relates to electrochemical cells, not nuclear changes.