The chemical formula is not specified, is a state of matter that is characterized by its low density and lack of definite shape or volume. Gases can be composed of individual atoms, such as in the case of noble gases like helium and neon, or they can be made up of molecules, such as oxygen gas (O2) or carbon dioxide gas (CO2).

Gases are able to freely move and fill any container they are placed in, as their particles are not tightly packed together like in solids or liquids. They also have the ability to expand and contract with changes in temperature and pressure.

Gases have several properties that distinguish them from other states of matter. These include:

1. Compressibility: Gases are highly compressible, meaning their volume can be reduced by applying pressure. This is due to the large spaces between gas particles.

2. Expansion: Gases can expand to fill the entire volume of a container. When heated, the gas particles gain energy and move faster, causing the gas to expand.

3. Diffusion: Gases have the ability to mix and spread out evenly through other gases. This is known as diffusion and is responsible for the spread of odors or the mixing of gases in the atmosphere.

4. Low density: Gases have a low density compared to solids and liquids. This is because the particles in a gas are much farther apart, resulting in a lower mass per unit volume.

Gases also exhibit various physical and chemical properties, depending on their composition. These properties include boiling point, melting point, solubility, and reactivity.

In summary, a gas is a state of matter characterized by its low density, lack of definite shape or volume, and the ability to expand, contract, and freely move. Gases play a crucial role in various natural and industrial processes, and their properties make them useful in many different applications.