The balanced chemical reaction is:
2H2+O2-->2H2O
To determine the mass of hydrogen that is needed, we need use the initial amount of oxygen and relate it to hydrogen from the reaction given. We do as follows:
192 g O2 ( 1 mol O2 / 32 g O2) ( 2 mol H2 / 1 mol O2 ) ( 2.02 g H2 / 1 mol H2 ) = 24.24 g H2
