Correct Answer - The Variability in oxidation state of transition matals is due to the incomplete filling of d-orbitals in such a way that their oxidation state differ from each other by unity e.g.,`Fe^(2+)` and `Fe^(2+)` and `Fe^(3+)` , Cu^(+) and `Cu^(2+)` etc. In case of non-transition elements. the oxidation states differ by units of two e.g., `Pb^(2+)` and `Pb^(4+)` , `Sn^(2+)` and `Sn^(4+)` etc. Moreover, in transition elements , the higher oxidation state are more stable for heavier elements in a group. In p-block elements , the lower oxidation state are more stable for heavier members due to inert pair effect, e.g in group- `16`,`Pb`(II) is more stable than `Pb(Pb)`.
