Chemistry - f-block Question with Solution | TestHub

In actinides, both $4f$ and $5f$ orbitals are present. These orbitals poorly shields the nuclear charge due to which the energy difference between the $5f$ and the $6d$ orbitals will be very low due to which the actinides will show a large number of oxidation states. Caution The elements in which the extra electron enters 5 - orbitals of $(n-2{)}^{\text{th }}$ shell (5f-block elements, actinides) shows the maximum oxidation state i.e. +7.