Which subatomic particle determines the stability of an atom? Which subatomic particle determines the atoms identify? Which subatomic particle (s) determine the atomic mass?

The neutron determines the stability of an atom. The proton determines the atoms identity. Both the neutron and proton determine the atomic mass of an atom.

Explanation:

The neutron determine an atoms isotope, and often its stability. The number of protons (which is shown on the periodic table) determine an atoms identity. Both of the neutrons and protons together in the nucleus make up the atomic mass.