The chemical symbol for the element "O" is O, which represents oxygen. It has an atomic number of 8 and is a vital element for life on Earth. Oxygen is a colorless, odorless gas at room temperature and is essential for respiration in most living organisms. It plays a crucial role in cellular processes that produce energy. In nature, oxygen is primarily found in the form of diatomic molecules (O2), but it is also present in compounds, such as water (H2O) and carbon dioxide (CO2). Oxygen constitutes about 21% of the Earth's atmosphere, supporting various ecosystems.