By the direct union of a metal with oxygen Some metals when heated in air or oxygen form the oxides of the metals. ... By the action of water or steam on some active metals Some active metals like sodium and potassium react with cold water to form hydroxides with the evolution of hydrogen gas.
On the basis of acidity bases can be classified into three types: monoacidic, diacidic and triacidic. Sodium hydroxide: NaOH Potassium hydroxide: KOH Calcium hydroxide: Ca(OH); 2 Rubidium hydroxide: RbOH
