H2 is the limiting reactant. To determine this, I used the balanced equation provided, the molar masses of H2 and O2, and the masses of reactants given. The molar mass of H2 is 2 g/mol and O2 is 32 g/mol, BUT there are 2 moles of H2 and only 1 mole of O2. That means the ratio of molar masses will be 4/32. Now we can determine what we have in excess with some algebra: 4/32 = 10/x -> x = 80

Here I used the mass given for H2 to determine how much O2 it could react with. Only 80 g of O2 will react with 10 g of H2 in this reaction.

Now with this information, you should be able to find the correct mass product :)