You should have included a reaction equation or some product so we can tell the balanced coefficients of nitrogen and hydrogen. Assuming you are producing ammonia, 3 moles of hydrogen are required for each one mole of nitrogen. These gases are diatomic.
50g Nitrogen / 28 g Nitrogen per mole = 1.786 moles of Nitrogen, therefore, 5.358 moles of Hydrogen gas. Thus, you need 5.358 moles times 2.0 g per mole = 10.7 g of Hydrogen