Question

________ form oxocation.
A) Lanthanides
B) Actinides
C) Noble gases
D) Alkali metals

Answer 1

We must know that the oxocation are the polyatomic cations containing one or more oxygen atoms. Actinides form oxocation whereas lanthanides cannot. The main difference is mainly due to the presence of a greater number of vacant d-orbitals in actinides and also they can vary their oxidation states more effectively than lanthanides.

Complete step-by-step answer:
Oxocations are the polyatomic cations containing one or more oxygen atoms or they are polyatomic ions with a positive charge that contains oxygen. Some examples are${\text{N}}{{\text{O}}^{\text{ + }}}{\text{,}}{{\text{O}}_{\text{2}}}^{\text{ + }}$.
Now, they ask among the inner transition metals, lanthanide and actinide series form oxocation and why? .Actinides form oxocation whereas lanthanides cannot. It is realised that actinides form oxocations formed due to high charge density. Also they have a greater number of vacant d orbitals; they can vary their oxidation states more effectively than lanthanides.
Actinides form complexes with ligands such as thio- ethers.
Some examples of oxocation are ${\text{U}}{{\text{O}}_{\text{2}}}^{{\text{2 + }}}\;$and ${\text{Np}}{{\text{O}}_{\text{2}}}^{{\text{2 + }}}$.
Also the noble gases have a closed-shell valence electron configuration and alkali metals have p orbitals only.
Therefore, we can conclude that the actinides only form oxocation.

The correct option is C.

Note: We must know that the lanthanide and actinide series form up the inner transition metals. In the lanthanide series the atomic number of elements starts from 58 and ends at 71. They have an electronic configuration of ${\text{6}}{{\text{s}}^{\text{2}}}$ in common to all but with variable occupancy of $4f$ level. That is in this series electrons fill their $4f$sublevel progressively. The actinides series the atomic number of are elements 89 to 103 and here they fill $\;5f$sublevel progressively. The main difference between actinides and lanthanides is that actinides can form complexes easily whereas lanthanides do not form complexes easily.