im just guessing....but if it takes 6 moles of Oxygen to react with 3 moles of Phosphorus then it should look something like this?
6O + 3P ---> Product
so then box it out
3.1g * (1 mole P/31 g P) * (6 mole O/ 3 mole P) * (16 g O/1 mole O) = 3.2 g of O...so I would choose D....am i correct?...if not that was only worth a shot