All oxides are not acidic in nature. There are oxides which are basic, neutral and amphoteric. The acidic nature is due to the non availability of donor protons. These oxides react with water to form an acid or with a base to form a salt. These oxides form either from non-metals or from metals which are in high oxidation states.

Examples of such oxides are Aluminium oxide, Silicon dioxide, Phosphorus oxides, Sulphur oxides, Chlorine oxides, etc..

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