3.28 x 10^6 atoms of oxygen.
If you are asking for the mass of the oxygen, first you would take Avagadro's constant to find out how many moles of oxygen there are. 3.28 x 10^6 / 6.022 x 10^23 . After this, you would get 5.44669545E-18 mol. Now, just multiply the mass of a mole of oxygen (same as atomic mass, but in grams) and you'll have the mass of oxygen. 8.71416805E-17 g