Which among the following non-metal is "monoatomic"?

Option 1 -> Oxygen exists as O₂ (diatomic molecule) under normal conditions.

Option 2 -> Chlorine exists as Cl₂ (diatomic molecule) under normal conditions.

Option 3 -> Nitrogen exists as N₂ (diatomic molecule) under normal conditions.

Option 4 -> Helium exists as He (single atoms) because it's a noble gas with a complete outer electron shell.

Hence, Option 4: Helium -> Noble gases like helium are monoatomic because they have stable, complete outer electron shells and do not need to bond with other atoms to achieve stability -> correct