Bases are usually: metal oxides, such as copper oxide. metal hydroxides, such as sodium hydroxide, or. metal carbonates, such as calcium carbonate.

Based on their acid-base characteristics oxides are classified as acidic, basic, amphoteric or neutral: An oxide that combines with water to give an acid is termed as an acidic oxide. The oxide that gives a base in water is known as a basic oxide.

The chemical formula for an oxide is O2− . An oxide ion is a negatively charged oxidation state of oxygen.

Examples include: Sodium oxide, which reacts with water to produce sodium hydroxide. Magnesium oxide, which reacts with hydrochloric acid to form magnesium chloride. Copper(II) oxide, which reacts with nitric acid to form copper nitrate.

Basic oxides are oxides that show basic properties in opposition to acidic oxides and that either

•reacts with water to form a base; or
•reacts with an acid to form a salt and water which called neutralization reactions.

eg. All oxides in Group 1 & 2 elements are basic (except BeO), they react with water to form a base.