When one mole ${\mathrm{NO}}_3^{-}$ is converted into 1 mole ${\mathrm{NO}}_2$,, 0.5 mole ${\mathrm{N}}_2$ and 0.5 mole ${\mathrm{N}}_2\mathrm{O}$ respectively, it  accepts x,y and z mole of electrons :$-x,y,z$ are  respectively