Question

1. what is the ratio of protons to neutrons that is in the stable range? 18. which elements are always unstable?

Explanation:

Step1: Proton - neutron ratio for stability

For light elements (atomic number \(Z<20\)), a stable proton - neutron ratio (\(p/n\)) is close to \(1:1\). As the atomic number increases (\(Z > 20\)), the stable \(p/n\) ratio increases to about \(1.5:1\). So the stable range is approximately \(1:1\) to \(1.5:1\).

Step2: Unstable elements

Elements with atomic number \(Z>83\) (bismuth and above) are always unstable because the electrostatic repulsion between protons becomes too great to be balanced by the strong - nuclear force, and they undergo radioactive decay.

Answer:

1. Approximately \(1:1\) to \(1.5:1\)
2. Elements with atomic number \(Z > 83\)