Which of the following pairs are classified as diatomic molecules?

Diatomic molecules are those that consist of two atoms, which can be of the same element or different elements. When considering the correct answer, chlorine and iodine are both elements that commonly exist as diatomic molecules in their natural forms.

Chlorine exists as Cl₂, meaning two chlorine atoms bond together to form a stable molecule. Similarly, iodine occurs as I₂, with two iodine atoms bonded together. These diatomic forms are significant because many elements will naturally pair up to achieve stability through bonding, and in the case of chlorine and iodine, this is observed as they tend to be found in molecular forms in the gas and solid states, respectively.

In contrast, while hydrogen is a diatomic molecule, helium is a noble gas that exists as individual atoms rather than a diatomic molecule. Similarly, nitrogen is diatomic as N₂, but argon is also a noble gas that does not form diatomic molecules. Oxygen and fluorine are diatomic molecules (O₂ and F₂, respectively), but chlorine and iodine are both halogens that commonly exist as diatomic molecules in nature. The choice of chlorine and iodine as diatomic molecules is made clear by their molecular forms and their tendency to bond with themselves.