Which of the following is an example of a diatomic molecule?

A diatomic molecule is one that consists of two atoms. This includes molecules made up of two atoms of the same element or different elements. In the case of option A, H2, it is a diatomic molecule because it is composed of two hydrogen atoms bonded together. This is one of the simplest diatomic molecules and is a prime example of this type.

The other choices include molecules composed of different quantities and types of atoms, thus not fitting the definition of diatomic. For instance, CO2 (carbon dioxide) contains three atoms in total; one carbon atom and two oxygen atoms, which makes it a triatomic molecule. NaCl (sodium chloride) is an ionic compound made of sodium and chloride ions, which aren’t classified as diatomic since they are not covalently bonded molecules and consist of ions rather than neutral molecules. CH4 (methane) is made up of one carbon atom and four hydrogen atoms, totaling five atoms, which means it is a tetratomic molecule, not diatomic.