Answer :
In order to make water (H2O) out of hydrogen (H2), you also need OXYGEN (O2) gas. So, first write a correctly balanced equation for this reaction.
2H2(g) + O2(g) ==> 2H2O
Now, convert 59.5 g of H2 to moles, then figure out moles of H2O and then moles of O2 used to do this.
moles H2 = 59.5 g H2 x 1 mole/2 g = 29.8 moles H2
moles H2O formed = 531 g H2O x 1 mole/18 g = 29.5 moles H2O
So, the mole ratio of H2 to H2O is 1:1 meaning that the moles of O2 used will be 1/2 that amount. This is the case because from the balanced equation you see that 1 O2 reacts with 2 H2 and produces 2 H2O.
Amount of O2 used = 29.8/2 = 14.9 moles