(a, b, c)

The great tendency of transition metal ions to form complexes is due to : (i) small size of the atoms and ions, (ii) high nuclear charge and (iii) availability of vacant d-orbitals of suitable energy to accept lone pairs of electrons donated by ligands.

The existence of the transition elements in different oxidation states is due to the participation of inner (n – 1) d-electrons in addition to outer ns-electrons because, the energies of the ns and (n – 1) d-sub-shells are nearly same.

The transition metals show magnetic properties due to presence of number of unpaired electrons in d-orbitals.

Most the transition metal ions are coloured, because they have unpaired electrons which can undergo d-d- transition in presence of ligands.