Answer:
Molecule
Step-by-step explanation:
A molecule is the smallest particle of a compound that retains its chemical properties i.e. a molecule is responsible for the chemical reactiveness of a compound. In other words, a molecule contains two or more atoms that are joined together by a chemical bond. For example, H2 is a molecule containing two hydrogen atoms.
In this question, chlorine gas with the molecular formula (Cl2) contains two atoms of chlorine held together by a chemical bond, hence, CHLORINE GAS is best described to be a MOLECULE.