To calculate the mass of 0.4 mole of oxygen atoms, we need to know the molar mass of oxygen and multiply it by the number of moles.
The molar mass of oxygen (O) is approximately 16.00 grams per mole (g/mol).
Now, we can calculate the mass as follows:
Mass of 0.4 mole of oxygen atoms = Molar mass of oxygen x Number of moles
Mass of 0.4 mole of oxygen atoms = 16.00 g/mol x 0.4 mole
Mass of 0.4 mole of oxygen atoms = 6.4 grams
Therefore, the mass of 0.4 mole of oxygen atoms is approximately 6.4 grams.