Oxide

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO. It is formed by an ionic bond between one magnesium and one oxygen atom. Magnesium oxide is hygroscopic in nature and care must be taken to protect it from moisture.

Manganese(II) oxide is the chemical compound with formula MnO. It occurs in nature as the rare mineral manganosite

Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, has a formula of HgO and a formula weight of 216.6. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form montroydite is very rarely found.

The yellow form can be obtained by precipitation of aqueous Hg2+ with alkali.[5] The difference in colour is due to particle size, both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an O-Hg-O angle of 108°.[5].