Oxygen is the most common elemental form of the element oxygen; its molecular formula is O₂, and its relative molecular mass is 32. Under standard conditions, two oxygen atoms bond to form oxygen gas-a colorless, odorless, and tasteless diatomic gas. Oxygen is a constituent of air, accounting for 20.9% of its volume. Oxygen is denser than air; under standard conditions, its density is 1.429 g/L. It is soluble in water, though its solubility is quite low-approximately 30 mL of oxygen dissolves in 1 liter of water. At a pressure of 101 kPa, oxygen transforms into a pale blue liquid at approximately -180°C, and into a snowflake-like, pale blue solid at approximately -218°C.
Oxygen acts as a strong oxidizing agent, capable of accepting electrons during chemical reactions. This characteristic allows it to play a pivotal role in numerous chemical processes, including combustion reactions, corrosion processes, and cellular respiration. Reactions involving oxygen and other substances typically release substantial amounts of energy, forming the basis for how biological organisms generate ATP (the cell's energy currency). Biologically, oxygen is a critical reactant consumed during cellular respiration; it is inhaled by organisms through the respiratory system and utilized to oxidize organic compounds, thereby releasing energy, carbon dioxide, and water. This process is fundamental to the survival of multicellular organisms, enabling them to sustain complex life functions.
In addition to sustaining human life, oxygen is widely utilized in medical rescue operations. Furthermore, oxygen is indispensable for the combustion of fuels and is extensively employed in various industrial applications, such as steelmaking, gas welding, chemical manufacturing, and space exploration.
