What is gas and examples?

Gas is one of the four fundamental states of matter, characterized by low density and high compressibility, where particles are widely spaced and move freely. Common examples of gases include oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂), all of which are essential for life and various chemical processes. Other examples include helium (He), used in balloons, and natural gas, primarily composed of methane (CH₄), which is used for heating and cooking. Gases can easily expand to fill their containers and do not have a fixed shape or volume.