O-18, an isotope of oxygen, has a stable nucleus. O-19, another isotope of oxygen, does not have a stable nucleus. Based on this information, which statement is correct?

A nucleus that is unstable is radioactive, while a stable nucleus is not radioactive. Therefore, O-19 is radioactive and O-18 is not. Both isotopes have nuclear binding energy and mass defect, so those differences do not distinguish them; O-18 also has 10 protons and 8 neutrons, not equal numbers.

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