how many grams of H are needed to produce 1.80grams of H2O

Answer 1

1.8 g H2O x (1 mol/18g) = 0.1 mol H2O. There are two moles H per mol H2O; therefore, 0.2 mol of H atoms.
0.2 x (1 g H/1 mol H) = 0.2 grams H needed.