Question

What is the maximum amount of water (in grams) that can be produced given 4 moles of hydrogen and 4 moles of oxygen?

Answer 1

2H2+O2>>>2H2O

four moles of H2 produces 4moles water
4moles water=4*18grams water

Answer 2

you need 2 mols of H2 for every mol of O2

2 H2 + O2 -> 2 H2O
or in this problem
4H2 + 2 O2 --> 4 H2O

H2 is 2+16 = 18 grams/mol
so
4 * 18 grams