Final answer:
Chlorine is the element from the list that normally exists as a gas of diatomic molecules, specifically as Cl₂.
Step-by-step explanation:
The element that normally exists as a gas of diatomic molecules from the options provided is chlorine. Chlorine, a halogen from Group 17, naturally exists as diatomic molecules with a molecular formula of Cl₂. The halogens are known for having seven valence electrons and tend to form diatomic molecules such as fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂). Other non-metal elements that form diatomic molecules include hydrogen (H₂), nitrogen (N₂), and oxygen (O₂).