The molar mass of oxygen (O) can be calculated by summing up the atomic masses of its constituent atoms. Oxygen has an atomic number of 8, which means it has 8 protons in its nucleus. The most common isotope of oxygen is oxygen-16 (with 8 protons and 8 neutrons), but there are also lesser abundant isotopes like oxygen-17 and oxygen-18.
Using the atomic masses of these isotopes, the molar mass of oxygen (O) can be calculated as follows:
(16.00 g/mol * 0.9976) + (17.00 g/mol * 0.00038) + (18.00 g/mol * 0.002) = 15.999 g/mol
So, the molar mass of oxygen is approximately 15.999 grams per mole (g/mol).
Therefore, the mass of 1.00 mole of oxygen is equal to its molar mass, which is approximately 15.999 grams.