Discuss the role of the nucleus in determining the identity and stability of an atom.

The nucleus determines the identity of an atom through its number of protons (atomic number), which uniquely defines the element. The number of neutrons in the nucleus influences the stability of the atom; certain proton-to-neutron ratios lead to stable isotopes, while others result in unstable, radioactive isotopes. The strong nuclear force within the nucleus holds the protons and neutrons together, preventing the nucleus from flying apart due to electrostatic repulsion between protons.