How many o2 molecules can be made with the oxygen from 492 g of sodium phosphate?

To answer this question, you need to change the sodium phosphate unit into mol and doing the reaction. Sodium phosphate or Na3PO4  molecular weight is 163.94 or 164 rounded up. Then the amount should be: 492g/ (164g/mol)= 3 mol

For every 1 mol of Na3PO4  there are 4 mol of oxygen element. To made 1 mol of O2 molecule, you will need 2 mol oxygen element. Then the amount of oxygen should be: 4/2 * 3 mol= 6 mol * 6.02 * 10^23= 36.12 * 10*23= 3.61 * 10^24