Chlorine (Cl₂) is the molecular element among the given choices as it exists naturally as a diatomic molecule.
The correct answer to the given question is option D.
To determine which of the given species is a molecular element, it's important to understand what a molecular element is.
A molecular element typically consists of two or more identical atoms bonded together. Therefore, the choices carbon dioxide (CO₂), neon (Ne), sodium (Na), and chlorine all must be considered.
Carbon dioxide, being a compound of carbon and oxygen, is not a molecular element but a molecular compound.
Neon is a noble gas and exists as a monoatomic molecule at room temperature and atmospheric pressure, making it a monoatomic element and not a molecular element.
Sodium is a metal and does not typically form molecules in its elemental form; it forms metallic bonds.
Chlorine, however, exists naturally as a diatomic molecule (Cl₂), making it a molecular element. Therefore, the molecular element among the choices listed is chlorine (Cl₂).