What causes radioactivity in atomic nuclei?

• A. An imbalance of neutrons and protons.
• B. A high-energy gamma emission alone.
• C. Excess electrons.
• D. Distorted electron orbit.

Answer: (A)

Radioactivity happens when the nucleus is unstable because the number of neutrons relative to protons isn’t in a favorable balance. That imbalance makes the strong nuclear forces less able to keep the nucleus stable, so it decays to a more stable configuration by emitting particles (like alpha or beta particles) and often gamma radiation as it moves to a lower-energy state. Gamma emission is something that occurs during this decay process, not the cause of instability itself. The arrangement of electrons—excess electrons or distorted electron orbits—affects chemistry and atomic structure but does not drive nuclear decay.