A monoxide is any oxide containing just one atom of oxygen in the molecule. For example, Potassium oxide (K₂O), has only one atom of oxygen, and is thus a monoxide. Water (H₂O) is also a monoxide; see dihydrogen monoxide hoax. A well known monoxide is carbon monoxide (CO); see carbon monoxide poisoning. Most of the members of the Periodic Table form oxides when oxidized. There are two main types of oxides: monoxides and dioxides. Monoxides (generally MO) such as silicon monoxide (SiO) only exist at high temperatures. Among monoxides, CO is neutral, GeO is distinctly acidic, and SnO and PbO are amphoteric.