Oxygen

Oxygen is the 8th Element of the Periodic Table. At the atmospheric pressure and temperature of the Earth it is in the form of a colourless, odourless dimeric gas, O₂, and makes up around 21% of the atmosphere. Atomically, oxygen contains 8 protons, 8 neutrons and 8 electrons when not in the form of an Isotope. It has a melting point of 54.36 K and a boiling point of 90.20 K. 

Oxygen plays an important role in the biological process of Respiration where it is used as a substrate in combination with Glucose to produce Carbon Dioxide and Water . It is also produced in the process of photosynthesis, where carbon dioxide and water are involved in the presence of light energy to form oxygen and glucose.