Question

Identify the incorrect statement from the following
A. D -Block elements show irregular and erratic chemical properties among themselves.
B. $La$ and $Lu$ have partially filled d orbitals and no other partially filled orbitals.
C. The chemistry of various lanthanoids is very similar.
D. $4f$ and $5f$ orbitals are equally shielded.

Answer 1

Hint: Lanthanoid contraction can be defined as the phenomenon where the outermost orbitals face or experience more attraction from the nucleus and thus contract or shrink in radius as these orbitals are not protected from the attractive force of the nucleus.

Complete step by step answer:
D block elements are known as the outer transition elements. They show irregular or erratic chemical behavior due to the fact they can show variable oxidation states. Therefore, the first option is correct.
$La$ and $Lu$ are present in the d block and f block respectively. Their electronic configurations are represented as follows:
La: $[Xe]5{d^1}6{s^2}$
Lu: $[Xe]4{f^{14}}5{d^1}6{s^2}$
In both these elements we see partially filled d orbitals. And we can say that option B is also correct.
The reason why the lanthanides mostly have the same chemical properties is due to the fact that they have elements that differ in the number of electrons that occupy the $4f$ orbitals and these electrons do not have that much influence on the properties of the elements. Also due to the phenomenon of lanthanoid contraction that was mentioned in the hint, find that the radius of all the ions belonging to this group are identical making their chemical properties also identical. This means that option c is also correct.
Thus we can conclude by inferring that the wrong statement among the following is option d. if we go on to explain why the statement is wrong we realize that the orbitals $4f$ and $5f$ belong to different shells. Thus, they cannot be equally shielded as $5f$ has lesser shielding than $4f$ because $4f$ is closer to the nucleus.

So, the correct answer is Option d.

Note: D orbitals have variable oxidation state because the differentiating electrons or valence electrons usually occupy the $\left( {n - 1} \right)d$ and $ns$ orbitals and these orbitals are extremely close to each other which leads to the ability of electrons to easily excited from one orbital to another.Shielding effect is least in f orbitals followed by d, p and s orbitals.