Oxygen is a chemical element with the atomic number 8 and the symbol O on the periodic table. It is a colorless, odorless, and tasteless gas that makes up about 21% of the Earth’s atmosphere. Oxygen is necessary for respiration and combustion, and it plays a critical role in sustaining life on Earth.

In respiration, organisms use oxygen to break down glucose and other molecules to produce energy in the form of ATP (adenosine triphosphate). This process, called aerobic respiration, occurs in the mitochondria of cells. Without oxygen, aerobic respiration cannot occur, and cells rely on anaerobic respiration, which is a less efficient way of producing energy.

Oxygen is also necessary for combustion, which is the process of burning. When a substance burns, it reacts with oxygen to produce heat and light. Combustion is used in many applications, such as generating electricity, heating homes, and powering vehicles.