Answer the question on the basis of passage given below:

In the periodic table, the d-block contains the elements of group 3 to 12. The d-orbitals are progressively filled in each of the four long periods. The elements of d-block referred as transition metals have partially filled d-orbitals and exhibit certain characteristic properties such as variety of oxidation states, formation of coloured ions, act as catalyst and slow paramagnetic behavior.

The two inner transition metals series 4f and 5f are known as Lanthanoids and Actinoids respectively. The lanthanoids resemble one another more closely as compared to ordinary transition in any series.

In context of the Lanthanoids, which of the following statements is NOT correct?

(A) There is a gradual decrease in the radii of the members with increasing atomic number in the series.

(B) Availability of 4f electrons results in the formation of compounds in +4 oxidation state for all the members of the series

(C)    Because of similar properties, the separation of lanthanoids is not easy

(D)   \(La(OH)_3\) is least basic among hydroxides of lanthanoids

(E)    \(Ce^{2+}\) can act as an oxidizing agent

Choose the correct answer from the options given below:

B  only

The correct answer is: (4) B only

Let us break down each statement:

(A) There is a gradual decrease in the radii of the members with increasing atomic number in the series.

This statement is correct. The lanthanoid series exhibits a phenomenon known as the "lanthanoid contraction," where there is a gradual decrease in the atomic and ionic radii as you move across the series from lanthanum to lutetium. This is due to poor shielding of the increasing nuclear charge by the inner 4f electrons.

(B) Availability of 4f electrons results in the formation of compounds in +4 oxidation state for all the members of the series.

This statement is incorrect. While the lanthanoids can exhibit a variety of oxidation states, they generally do not form compounds in the +4 oxidation state. The most common oxidation states for lanthanoids are +3 and sometimes +2.

(C) Because of similar properties, the separation of lanthanoids is not easy.

This statement is correct. Lanthanoids have similar chemical properties due to the filling of their 4f orbitals, which makes their separation challenging. They often occur together in natural ores and have similar behaviors in chemical reactions, making it difficult to isolate individual lanthanoid elements.

(D) \(La(OH)_3\) is least basic among hydroxides of lanthanoids.

This statement is generally correct. Lanthanum hydroxide (La(OH)3) is less basic compared to the hydroxides of other lanthanoids because it has a larger ionic radius, which results in weaker bonding between the lanthanum ions and hydroxide ions.

(E) (Ce^{2+}\) can act as an oxidizing agent.

This statement is correct. Cerium in the +2 oxidation state \((Ce^{2+})\) can readily undergo oxidation to the +3 oxidation state. This property allows cerium to act as an oxidizing agent in certain chemical reactions.

So, the statement that is NOT correct is option (B), as lanthanoids typically do not form compounds in the +4 oxidation state.