Can react with acid to form salt and water, this kind of oxide is called basic oxides (and the product can only have salt and water, can not have any other substances generated). Basic oxides include active metal oxides and low-valent oxides of other metals, such as Na2O, CaO, BaO and CrO, MnO.The corresponding hydrates of basic oxides are bases. For example, the corresponding hydride of CaO is Ca(OH)2, and the corresponding hydride of Fe2O3 is Fe(OH)3. oxides of alkali metals and calcium, strontium, and barium can react with water to form the corresponding hydroxides. They are all strong bases:

Na2O + H2O==2NaOH

CaO + H2O==Ca(OH)2

At high temperatures, alkaline oxides interact with acidic oxides to form salts:

CaO + SiO2==CaSiO3

Alkaline oxides are more stable when heated and do not generally decompose.

Alkaline oxides are all metal oxides, which are not necessarily alkaline oxides, e.g. Mn2O7 is an acidic oxide and Al2O3 is amphoteric.

Oxides that react with water to form a corresponding base are basic oxides. Basic oxides are usually metal oxides.

But some metal oxides are not basic oxides.

Such as

Mn2O7 (acidic oxide)

Al2O3 (amphoteric oxide)

Na2O2, (peroxide)

KO2 (superoxide) and so on.