In Haber’s process, gaseous nitrogen and hydrogen react to form ammonia which has a volume that is _ times smaller than that of the reactants (N.T.P.)

Avogadro's law says that equal volumes of gases at constant temperature and pressure contain equal number of molecules. Reaction in Haber's process (consider that pressure and temperature are constant):

${\mathrm{N}}_2+3{\mathrm{H}}_2\to 2{\mathrm{NH}}_3$

Total volume of NH₃ is 2L and volume of reactants (N₂ and H₂) is 4L.

This implies that volume of NH₃ is 0.5 times less than the volume of reactant.