Answer :
first of all, you should write down a balanced equation for the reaction
3H2 + N2 ----> 2NH3
convert from grams of NH3 ----- moles NH3------moles H2------g H2
11.21 gNH3 / ( 17g/ mol NH3)* (3 moles of H2/ 2 moles of NH3) * (2 g H2/ mol H2)
3H2 + N2 ----> 2NH3
convert from grams of NH3 ----- moles NH3------moles H2------g H2
11.21 gNH3 / ( 17g/ mol NH3)* (3 moles of H2/ 2 moles of NH3) * (2 g H2/ mol H2)