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?
For the answer to the question above, we are given with two isotopes of oxygen, one that is stable O-18 and O-19 that is unstable. The stability of a nucleus is relative to the nuclear binding energy and mass defect. In this case, nuclear binding energy is always. So the answer is O-19 has a mass defect; O-18 does not have a mass defect.