Thank you for reporting, we will resolve it shortly
Q.
The variability of oxidation state
The d-and f-Block Elements
Solution:
(d) The variability of oxidation states is a characteristic of transition elements. It arises due incomplete filling of $d$-orbitals in such a way that their oxidation states differ from each other by unity, e.g. $V ^{ II }, V ^{ III }, V ^{ IV }, V ^{ V }$. This is in contrast with the variability of oxidation states of non-transition elements where oxidation states normally differ by a unit of two.