To calculate the magnetic moment of the complex, we need to determine the number of unpaired electrons in the iron III ion. Iron III has an oxidation state of +3, so its electronic configuration will be different from that of the neutral iron atom.The electronic configuration of a neutral iron atom Fe is [Ar] 3d^6 4s^2. When it forms the Fe III ion, it loses three electrons, resulting in the electronic configuration [Ar] 3d^5.Now, we can use the formula for calculating the magnetic moment based on the number of unpaired electrons n : = n n+2 In the case of Fe III , there are 5 unpaired electrons n=5 : = 5 5+2 = 5 7 = 35The magnetic moment of the complex formed between iron III ion and ethylenediamine ligand en with a coordination number of 6 is approximately 35 Bohr magnetons BM .