The stability of atomic nuclei relies on the forces within the atom that balance out the charge. The electrons have the power to make an atom negatively or positively charged, but neutrons allow the atom to be electrically neutral regardless. The gravitational pull of protons and neutrons in the atomic nuclei keeps the electrons in an orbit, and with less protons than neutrons, electrons will be pulled into the nuclei and make the atom unstable; with less neutrons than protons, the electrons will be repelled and make the atom unstable. Therefore, the number and ratio of protons to neutrons are the factors that make an atom stable.
Answer: ratio of neutrons to protons and number of protons and neutrons
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