Question

Actinoid contraction is more than lanthanoid contraction because:
(A) Energy of $4f$ and $5f$ orbitals are same
(B) $5f$ orbitals are more diffused as compared to $4f$ orbitals
(C) Actinoids show greater range of oxidation states than lanthanides.
(D) Actinides are highly reactive.

Answer 1

Hint : Lanthanides and actinides are the $f$ block elements, and they are known as the inner transition elements due to their location in the periodic table which is intern because of their electron configurations. The $f$ orbitals can only hold a limit of fourteen electrons.

Complete Step By Step Answer:
Lanthanides are the rare earth elements on the periodic table, with atomic numbers ranging from $57$ to $71$ , starting from the element Lanthanum. The Actinide series, also known as the actinides, consists of elements with atomic numbers ranging from $89$ to $103$ .
Lanthanide contraction is the gradual reduction in the size of the atoms and ions of the lanthanide elements with the increasing atomic number from lanthanum to lutetium. Similarly, Actinoid contraction is the steady reduction in the ionic radii and the size of the atoms and ions, as the atomic number of actinides increases.
$5f$ orbitals are larger than $4f$ orbitals. So, $5f$ orbitals are more diffused, resulting in a weak shielding effect. As a result, having a smaller size allows for a more powerful nuclear charge. As a result, actinide contraction is greater than lanthanide contraction.
Thus, the correct option is $B$ which is $5f$ orbitals are more diffused as compared to $4f$ orbitals .

Note :
The Lanthanide and Actinide series are also known as Rare Earth Metals. The actinide series elements all have a wide spectrum of oxidation numbers and are all radioactive.
Lanthanide contraction and Actinoid contraction is a distinct property of the $f$ block elements.