A compound consisting of two elements, one of which is oxygen. The substances that can react with oxygen are called oxides. According to their chemical properties, oxides can be divided into acidic oxides and alkaline oxides.

First, the classification of oxides: 

Not salt oxides -CO, NO 2. Salt oxides:

① acid oxides; 

② basic oxide; 

③ amphoteric oxide; 

④ Complex oxides (Fe3O4, P3O4, peroxide, superoxide)

Concept Analysis:

① Non-metallic oxides are not necessarily acid oxides; Such as NO, CO(non-salt oxide), NO2, N2O4, H2O

② Acid oxides are not necessarily non-metallic oxides; Such as Mn2O7, CrO3

③ Metal oxides are not necessarily basic oxides; Such as Al2O3, ZnO(amphoteric), Mn2O7, CrO3(acid oxide)

④ Basic oxides must be metal oxides.

⑤ Anhydride is not necessarily an acid oxide; Such as acetic anhydride (CH3CO)2O and so on

⑥ Acid oxides must be anhydrides.

⑦NO2 - because of the reaction with alkali not only to form salt and water, and NO, so it is not acid oxide; 

⑧Na2O2 - because of the reaction with acid not only to produce salt and water, and O2, so it is not basic oxide.