A stable nucleus (light with A < 10) has

Nuclear stability is governed by the ratio of neutrons (N) to protons (Z). For light nuclei, specifically those with an atomic number (Z) less than 20, stability is generally achieved when the number of protons and neutrons are approximately equal, resulting in an N/Z ratio of 1 [t2][t3][t6]. In this range, the nuclear force effectively balances the relatively small Coulomb repulsion between protons [t3]. For example, stable light isotopes like Helium-4 (2p, 2n), Carbon-12 (6p, 6n), and Oxygen-16 (8p, 8n) follow this 1:1 trend. While very light exceptions like Hydrogen-1 (no neutrons) and Helium-3 (more protons) exist, the general rule for stable light nuclei (A < 10) is having exactly or nearly the same number of neutrons and protons [t1][t2]. As the mass number increases beyond this range, more neutrons are required to provide additional binding force to counteract increasing electrostatic repulsion [t3][t6].