Final answer:
Among the elements neon, chlorine, hydrogen, and fluorine, neon is the most stable due to its full outer electron shell, which is a characteristic of noble gases. This configuration means neon has a low reactivity compared to the others, making it the most stable.
Step-by-step explanation:
Among the elements listed, neon (Ne) is the most stable. Neon is a noble gas, which means it has a full outermost energy level. It has all of its energy orbitals full, making it very stable and unreactive.
On the other hand, chlorine (Cl), hydrogen (H), and fluorine (F) are not as stable as neon. Chlorine is a halogen, hydrogen is not a noble gas and does not have all its energy orbitals full, and fluorine is a highly reactive element.