As for $\mathrm{N}{\mathrm{H}}_3$ the force of attraction between $\mathrm{N}{\mathrm{H}}_3$ molecules is maximum (Van der Waal constant 'a' is high) as it is polar so dipole-dipole interaction are maximum hence it shows maximum deviation. ${\mathrm{N}}_2,\mathrm{C}{\mathrm{H}}_4,{\mathrm{H}}_2$ are non-polar so their deviation is less than ammonia.