Atoms with certain characteristics are radioactive. which of those below will always be radioactive?

All atoms with an atomic number over 83

Explanation:

The electromagnetic repulsion of the protons in the nucleus is overcome by strong nuclear forces that keep the nuclear particles together. However, as the atomic number gets bigger so does the size of the nucleus. Therefore, the repulsive electromagnetic forces become greater than the nuclear forces hence the atom becomes unstable. Instability of the nucleus means the atoms become naturally radioactive.

option a and d is the correct answer

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