Question

Oxocations are formed by:
A) Lanthanides
B) Actinides
C) Noble gases
D) Alkali metals

Answer 1

We know that the polyatomic cations that contain one or more oxygen atoms are known as oxocations. To form the oxocations the elements must have more number of vacant d-orbitals, variable oxidation state and high charge density.

Complete step by step answer:
We know that the polyatomic cations that contain one or more oxygen atoms are known as oxocations. Also, oxocations can be defined as the polyatomic ions that contain one or more oxygen atoms along with positive charge.
Examples of oxocations are: ${\text{N}}{{\text{O}}^ + }$, ${\text{O}}_2^ +$.
Consider lanthanides. We know that the atomic numbers of lanthanides range from 58 to 71. The general electronic configuration of lanthanides is $4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$. The energies of the 4f and the 5d orbitals are almost equal. Thus, the electrons enter the 4f orbital and the 5d orbital remains vacant.
The number of vacant d-orbitals of lanthanides is less. Also, lanthanides do not show variable oxidation state. The highest oxidation state shown by lanthanides is +4. Lanthanides have low charge density. Thus, oxocations are not formed by lanthanides.
Thus, option (A) is not correct.
Consider actinides. We know that the atomic numbers of actinides range from 90 to 103. The general electronic configuration of actinides is $5{f^{1 - 14}}6{d^{0 - 1}}7{s^2}$. The energies of the 5f and the 6d orbitals are almost equal. Thus, the electrons enter the 5f orbital and the 6d orbital remains vacant.
The number of vacant d-orbitals of actinides is more. Also, actinides show variable oxidation state. The highest oxidation states shown by actinides are +4, +5 and +6. Actinides have high charge density. Thus, oxocations are formed by actinides.
Thus, option (B) is correct.
Consider noble gases. We know that the elements of group 18 i.e. helium, neon, argon, krypton, xenon and radon are the noble gases. The general electronic configuration of noble gases is $n{s^2}n{p^6}$. Noble gases have stable electron configurations.
The noble gases have a closed-shell valence electron configuration i.e. the valence shell of noble gases are completely filled. Thus, oxocations are not formed by noble gases.
Thus, option (C) is not correct.
Consider alkali metals. We know that the elements of group 1 i.e. lithium, sodium, potassium rubidium, cesium and francium are the alkali metals. The general electronic configuration of alkali metals is $n{s^1}$.
The alkali metals do not have d-orbitals. Thus, oxocations are not formed by alkali metals.
Thus, option (D) is not correct.
Thus, oxocations are formed by actinides.

Thus, the correct option is (B) actinides.

Note: The atomic numbers of actinides range from 89 to 103. The general electronic configuration of actinides is $5{f^{1 - 14}}6{d^{0 - 1}}7{s^2}$. The energies of the 5f and the 6d orbitals are almost equal. Thus, the electrons enter the 5f orbital and the 6d orbital remains vacant. Examples of oxocations formed by actinides are: ${\text{UO}}_2^{2 + }$, ${\text{NpO}}_2^{2 + }$.