• Acidic Oxides (Acid Anhydrides;酸酐): O- X bond is strong and covalent.SO2, NO2, CO2• When H- O- X grouping is dissolved in water, the O- X bond will remain intact. It will be the polar and relatively weak H- O bond that will tend to break, releasing a proton• Basic Oxides (Basic Anhydrides): O- X bond is ionic.K2O, CaO• If X has a very low electronegativity, the O- X bond will be ionic and subject to being broken in polar water, producing a basic solution