All metallic oxides that react with water to form a base solution are considered basic anhydrides, including lithium, magnesium, sodium and calcium oxides. Only the oxides formed by the alkali metals and alkali earth metals, Groups I and II on the periodic table respectively, are basic anhydrides.
When these metal oxides come into contact with water, they react to form their corresponding hydroxide. For instance, the anhydride calcium oxide forms calcium hydroxide. All of the basic anhydrides, which have a very high charge and small size, can be produced by removing the water from their corresponding hydroxide at high temperatures.