Valence bond theory successfully explains the magnetic behaviour of complexes. The substances which contains unpaired electrons are paramagnetic and paramagnetic character increases as the number of unpaired electrons increases, Magnetic moment of a complex can be determined experimentally and by using formula and we can detemine the number of unpaired electrons in it. This information is important in writing the electronic structure of complex which in turn also useful in deciding the geometry of complex.

(i) The magnetic moments (spin only) of [Ni(Cl) 4 ] 2– and [Ni(CN) 4 ] 2– are –