Metal oxides are basic
Metal oxides are basic; they react with water to form bases such as hydroxides.
E.g. sodium oxide + water → sodium hydroxide
Na2O + H2O → 2NaOH
Other examples of metal oxides include potassium oxide K2O and calcium oxide CaO.
Non-metal oxides are acidic
Because metal oxides are basic, non-metal oxides are acidic. They react with water to form acids.
E.g. carbon dioxide + water → carbonic acid
CO2 + H2O → H2CO3