The transition metal complexes are known to be paramagnetic in character. CFT helps us to understand the magnetic properties in terms of magnetic susceptibility measurements. The magnetic property of a substance depends upon the oxidation state, electronic configuration, co-ordination number of central metal and the nature of ligand field. An unpaired electron because of its spin is equivalent to an electric current flowing in a circular conductor. Hence, it behaves as a magnet. The magnetic moment will thus be expressed as Here, e = charge of an electron,m = mass of electron, h = planck's constantand c = velocity of light.The value of obtained from the above expression is 9.274 × 10^{-21} ergs gauss-1. This is taken as a unit of magnetic moment called Bohr magneton (B.M.)A substance containing one or more unpaired electrons has a definite value of magnetic moment and is attracted in external magnetic field. Such substances are called paramagnetic substances. On the other hand those substances having paired electrons will have zero magnetic moment and hence do not possess magnetic properties. These are known as diamagnetic substances.The magnetic moment of a substance depends upon the number of unpaired electrons i.e. greater is the number of unpaired electrons more is the magnetic moment. It has been shown that the magnetic moment of a substance containing 'n' unpaired electrons is approximately given by the expression below:Magnetic moment, Bohr magnetons.Magnetic moment is also given mathematically as, (here S = sum of spins of electrons) Or (? value of gyromagnetic ratio = 2.0)This relationship is used to calculate the number of unpaired electrons in an ion.From the knowledge of a number of unpaired electrons and the value of magnetic moment () it is possible to find Valence state of the metal ion is a given complex. Natures of bonding in the complex i.e. spin free or spin-paired type.The values of n calculated by this expression for different magnetic moments are given in the table below: