the balanced equation for the reaction is
N₂ + 3H₂ --> 2NH₃
since number of moles of gas is directly proportional to volume of gas once all other parameters are kept constant
the volume ratio of reactant gases is equal to molar ratio
therefore volume ratio of H₂ to NH₃ is 3:2
so 3 L of H₂ reacts to produce 2 L of NH₃ assuming N₂ is in excess
when 3.6 L of H₂ reacts - 2/3 x 3.6 L = 2.4 L of N₂ is formed
So 2.4 L of NH₃ is produced