The equation says we need 3 moles of H2 for every 2 moles of NH3 produced.
Convert 33.9 g of NH3 to moles by dividing by it's molar mass.The molar mass is 17 g/mole, so that means we have 33.9
g/7 g/mole or 1.94moles NH3. To get this amount of NH2, we need to adjust by the molar ratio of the H2/NH3, which is 3/2:
(3 moles H2)/(2 moles NH3) * (1.84 moles NH3) = 2.91 moles H2. Multiply by the molar mass of H2 to find grams. I get 5.82 grams.