The molar mass of molecular oxygen O2 is 32 g/mol. This means that 1 mole of oxygen, containing a number of molecules equal to Avogadro's constant, weighs 32 grams.
Oxygen is a colorless gas and is one of the major constituents of the Earth's atmosphere, along with molecular nitrogen N2. It plays an important role in biology as a major component of the processes of photosynthesis and respiration. Molecular oxygen facilitates the combustion of organic compounds, an oxidation reaction that produces carbon dioxide, water vapors and heat. For this reason, concentrated amounts of oxygen may be hazardous if they can come in contact with open flames.