the balanced equation for the formation of ammonia is as follows
N₂ + 3H₂ --> 2NH₃
stoichiometry of H₂ to NH₃ is 3:2
in gases number of moles of gas is directly proportional to volume of gases.
therefore molar ratio is equal to volume ratios.
this means volume ratio of H₂ to NH₃ is 3:2
volume of H₂ reacted - 54.1 L
if 3 L of H₂ forms - 2 L of NH₃
then 54.1 L of H₂ forms - 2/3 x 54.1 = 36.1 L of NH₃
volume of NH₃ formed is 36.1 L