Oxygen, represented by the symbol O, is a chemical element essential for life on Earth. It is a colorless, odorless gas that makes up about 21% of the Earth's atmosphere. Oxygen is crucial for the process of cellular respiration, where living organisms convert food into energy. In addition to its role in supporting life, oxygen is also involved in various chemical reactions, including combustion. It readily forms compounds with other elements, such as water (H2O) and carbon dioxide (CO2). Oxygen is vital for many industrial processes and is used in medical applications, such as oxygen therapy for patients.