When 46 grams of water are produced how many grams of oxygen must react according to the equation 2h2+o2=2h2o

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

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.