The correct response regarding stable isotopes is:
A stable nucleus has a similar number of protons and neutrons.
However, it's important to clarify that while stable nuclei often have a balanced ratio of protons and neutrons, there are exceptions in heavier elements where the number of neutrons can exceed the number of protons and still be stable. The other statements are false:
- Isotopes are not always unstable; many isotopes are stable.
- Not all isotopes with more neutrons than protons are stable; stability can vary based on the specific isotope.
- Some naturally occurring isotopes are stable, while others are radioactive.
Thus, although the first statement is the closest to being true, it is not entirely accurate as a blanket statement regarding all stable isotopes.