It's second to fluorine. And we'll talk more about fluorine when we'll talk about the seven A group elements or the halogens. Now, oxygen, like carbon, also forms strong bonds, strong double bonds. And oxygen exists in nature in a diatomic or a triathlonic form, namely ozone or O two oxygen. Now, O two, or oxygen, reacts with metals, alkaline metals and earth metals and transition metals to form metal oxides. Now, whenever our alkaline metals react with our oxygen, they form peroxide, for example, li two or ma two, et cetera.