The equation that describes the reaction between Na and O2 is as follows:
4Na + O2 ......> 2Na2O
Using the periodic table:
molar mass of Na = 23 grams
molar mass of O2 = 2*16 = 32 grams
molar mass of Na2O = 2(23) + 16 = 62 grams
From the balanced reaction:
32 grams of oxygen are required to produce 2*62 = 124 grams of Na2O.
Therefore, to know the amount of O2 that would produce 75 grams of Na2O, we will simply use cross multiplication as follows:
mass of O2 = (32*75) / 124 = 19.35483871 grams