An oxide that exhibits the property of a base is called a basic oxide. Since they are basic, they react with an acid to form a salt. These oxides are formed by the reaction of Oxygen with metals like Magnesium(Mg), Sodium (Na), etc. Basic oxide reacts with water to form a base as shown in the reaction below. Example of basic oxide: Magnesium oxide (MgO), CaO, K2O, Na2O.