I. [Fe(CN)6]4− Atomic number of Fe=26 Ground state configuration of Fe=[Ar]3d64s2 Fe2+=[Ar]3d6 Since, cyanide is a powerful ligand, therefore, all the electrons will be paired. Number of unpaired electrons in [Fe(CN)6]4−=0 II. [Fe(H2O)6]2+ Atomic number of Fe=26 Ground state configuration of Fe=[Ar]3d64s2 Fe2+=[Ar]3d6 Number of unpaired electrons in [Fe(H2O)6]2+=4. III. [Co(H2O)6]2+ Atomic number of Co=27 Ground state configuration of Fe=[Ar]3d74s2 Co2+=[Ar]3d7 Number of unpaired electrons in [Co(H2O)6]2+=3 So, the correct order is II > III > I.