Final answer:
Unstable nuclei undergo radioactive decay to achieve stability by emitting particles. The balance between protons and neutrons determines the stability of isotopes.
Explanation:
Unstable nuclei are nuclei that contain an excess of neutrons, making them prone to radioactive decay to achieve stability. During radioactive decay, unstable nuclei emit particles such as alpha or beta particles until they reach a more stable configuration. The stability of isotopes is determined by the balance between protons and neutrons in the nucleus, with the 'band of stability' used to identify stable isotopes.
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