Which condition most often leads to an unstable isotope?

An unstable isotope is often characterized by a high neutron to proton ratio. This condition occurs because isotopes with too many neutrons relative to protons can lead to an imbalance in the forces that hold the nucleus together. Neutrons play a crucial role in adding stability to the nucleus by offsetting the repulsive forces between protons, which are positively charged. However, when there are excessively high numbers of neutrons, the nucleus cannot maintain stability, leading to various forms of radioactive decay as the isotope attempts to reach a more stable state.

In contrast, a low neutron to proton ratio typically leads to instability due to insufficient neutrons to counteract the repulsion among protons, while an equal number of neutrons and protons is generally associated with more stable isotopes. Increasing electron count is irrelevant to the stability of isotopes, as electrons do not affect the nuclear forces at play within the nucleus.