The correct answer is C. fluorine.
A diatomic molecule is a molecule that is made up of two atoms of the same element. Examples of diatomic molecules include oxygen (O2), nitrogen (N2), hydrogen (H2), and fluorine (F2).
Argon (Ar) is a noble gas that is monatomic, meaning that it is made up of a single atom. Helium (He) is also a noble gas that is monatomic. Methane (CH4) is a hydrocarbon that is made up of one carbon atom and four hydrogen atoms.
Fluorine (F2) is a diatomic molecule that is made up of two fluorine atoms. The fluorine atoms are held together by a covalent bond, which is a type of chemical bond that is formed when two atoms share electrons.
The other options are not diatomic molecules because they are either monatomic or polyatomic. Monatomic molecules are made up of a single atom, while polyatomic molecules are made up of more than two atoms.