The particle unit of a chlorine gas would be Cl2. It is a diatomic molecule which means that it would exist as a molecule consisting two atoms of different or the same elements. In nature, chlorine gas cannot be readily found or obtained. It can be obtained as a by-product or the main product in chemical reactions. It can be obtained from the electrolytic process of sodium chloride resulting to the production of chlorine gas, NaOH and hydrogen gas where all of the products are highly reactive. Chlorine gas is a very toxic substance to living organisms when present in the body.