Answer:
because of energy difference between (n1)d and ns orbitals (sub levels) and involvement of both orbital in bond formation
Explaination:
the reason is that there is a difference in energy of orbitals of an atom of transition metal, so there (n1)d orbitals and there ns orbitals both make a bond and for this purpose they lose an electron that is why both sublevels shows different oxidation state.
Hope this helped you
