The chemical composition of ammonia is NH3. One mole of any gas has the same number of atoms or molecules (as the case may be).
To form one mole of ammonia we required one mole of nitrogen atoms or half a mole of nitrogen molecules, as nitrogen gas has the composition N2.
Assuming that the ammonia produced and the nitrogen gas used as a reactant initially are at the same temperature and pressure, a mole of either of them has the same volume.
As we have to produce 83.5 L of ammonia we need 83.5/2 = 41.75 L of nitrogen.
It is not possible to give a result in terms of the number of moles of gas required as we are only given the volume of the gas and no information on the temperature or the pressure has been provided.
The reaction requires 41.75 L of nitrogen gas.