the balanced equation for the formation of water is as follows
2H₂ + O₂ ---> 2H₂O
molar ratio of oxygen to water is 1:2
mass of water produced is - 46 g
therefore the number of moles of water produced - 46 g / 18 g/mol = 2.56 mol
1 mol of oxygen reacts to give 2 mol of water assuming oxygen is the limiting reactant
for 2 mol of water to be produced 1 mol of oxygen has to react
therefore for 2.56 mol of water to be produced - 1/2 x 2.56 mol = 1.28 mol of oxygen should react
mass of oxygen reacted is - 1.28 mol x 32 g/mol = 41.0 g
mass of oxygen that should react is 41 g