1. Acid oxide: an oxide that can react with water to form an acid or with alkali to form a salt, usually an oxide of nonmetallic elements and a high-valent oxide of some transition metal elements.

2. Basic oxide: It can react with acid to form salt and water. This kind of oxide is called basic oxide.

3. Basic oxides include oxides of active metals and suboxides of other metals.

4. Acid can react with basic oxides or some metal oxides, acid can react with some salts to generate acid and another new salt, alkali can neutralize acid, alkali can react with some salts to generate new salts and new bases, some salt solutions can react with metals, and some soluble salts can react with soluble bases.