Oxygen is a chemical element with the symbol **O** and atomic number **8**. It is a vital component of Earth's atmosphere, making up about 21% by volume. Oxygen is essential for respiration in most living organisms and is involved in combustion processes. Here are some key facts about oxygen: 1. **Physical Properties**: Oxygen is a colorless, odorless, and tasteless gas at room temperature. It is highly reactive and forms compounds with most elements. 2. **Role in Life**: It is crucial for the respiration of aerobic organisms, including humans. The body uses oxygen to produce energy by breaking down glucose in the cells. 3. **Discovery**: Oxygen was discovered by Joseph Priestley in 1774 and independently by Carl Wilhelm Scheele. It was later named by Antoine Lavoisier, who recognized its role in combustion and respiration. 4. **Chemical Reactivity**: Oxygen readily combines with many elements to form oxides. For instance, when oxygen combines with hydrogen, it forms water (H₂O). 5. **Ozone (O₃)**: In the upper atmosphere, oxygen exists as a molecule of three atoms (O₃), known as ozone, which absorbs harmful ultraviolet radiation from the sun, protecting life on Earth. Oxygen is indispensable not only for life but also for numerous industrial and medical applications, including the production of steel, water treatment, and as a component in medical breathing gases.