ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

A stable atomic nucleus is significant because it indicates a proper balance between protons and neutrons within the nucleus. This balance is crucial for maintaining nuclear stability; an unstable nucleus often has an excess or deficiency of one of these particles, leading to radioactivity and decay. The strong nuclear force binds protons and neutrons together, and this force must effectively counteract the electrostatic repulsion between protons. As such, a stable ratio of protons to neutrons is important for the integrity of the nucleus, preventing it from undergoing radioactive decay.

In contrast, a nucleus composed only of neutrons would not exist in a stable form, as neutrons cannot bind together without protons. The excessive energy release refers to nuclear reactions rather than stability and is not a trait of stability itself. While atomic mass number is related to the count of both protons and neutrons, it does not directly reflect the stability of the nucleus; indeed, different isotopes of atoms with the same atomic mass can exhibit varying degrees of stability.