Oxygen makes up 21% of the atmosphere and is vital to life on earth. It is the most abundant element on Earth and fifth most abundant in the universe. The presence of Oxygen is due to the process of photosynthesis from plants. This is an important process as most living organisms on earth rely on Oxygen for respiration and the creation of energy in living cells. In commercial uses Oxygen is used in hospitals and by divers and has industrial uses such as welding and oxidation of metals. Oxygen also exists as the allotrope Ozone that has the formula O3. Ozone is in the upper atmosphere and is responsible for protecting the earth from harmful UV rays. It is located in Group 16. It is a non metal gas at room temperature and it has a melting point of -218°c and a boiling point of -183°c. Oxygen was discovered by Carl Wilhelm Scheele, a Swedish pharmacist producing it from Mercuric oxide using Nitrates.
Joseph Priestly, Carl Wilhelm Scheele