Which is true about stable isotopes?

The correct statement regarding stable isotopes is:

**D. A stable nucleus has a similar number of protons and neutrons.**

This statement is generally true as stable isotopes tend to have a balanced ratio of protons to neutrons, which contributes to their stability.

Here is a brief explanation of why the other options are incorrect:

A. This is false because not all isotopes are unstable; many are stable and do not undergo radioactive decay.

B. This is false because there are many naturally occurring isotopes that are stable, such as carbon-12 and oxygen-16.

C. This is false because isotopes with more neutrons than protons are not necessarily stable; there are many that are unstable and radioactive. Stability depends on the specific ratio and the overall nuclear forces at play.