(i) In [Fe(H2O)6]+2. the oxidation state of Fe is +2 . The outermost electronic configuration of Fe is 3d64s24p0 . HO is weak field ligand and does not cause pairing up of electrons.
In this complex, there are 4 unpaired electrons. Therefore, it involves sp3d2 hybridisation and is paramagnetic.
(ii) In [Fe(CO)5] , the oxidation state of Fe is zero. The outermost electronic configuration of Fe is 3d64s24p0. CO is strong field ligand, causes pairing up of 4s -electrons into the 3d -orbitals.In this complex, there is no unpaired electron.
Therefore, it involves dsp p3 hybridisation and is diamagnetic.