Question

The most common oxidation state of actinides is
    (A) $+$2
    (B) $+$1
    (C) $+$3
    (D) $+$4

Answer 1

Hint: The actinides generally show multiple oxidation states. The oxides of actinoids which has the most common oxidation state are isostructural and have a general formula ${ M }_{ 2 }{ O }_{ 3 }$ where M is the actinide element.

Complete step by step solution:
-As we know actinides are the second inner transition which belongs to F block. It has a terminal electronic configuration of $\left[ Rn \right]5{{f}^{1-14}}6{{d}^{0-1}}7{{s}^{2}}$ where $\left[ Rn \right]$ is the electronic configuration of nearest noble gas Radon.
-Actinides show a greater variety in its oxidation states starting from $+$2 to $+$7. This happens due to the very small energy gap between 5f, 6d and 7s subshells.
-The oxidation state becomes increasingly more stable as the atomic number increases in the actinide series.
-$+3$ is the most common oxidation state of actinides. The $+$4 oxidation state is the most stable in Thorium and Plutonium. $+$5 is common in Protactinium and Neptunium. The $+$6 oxidation state is seen in Uranium. As we can see, in actinides, the distributions of oxidation states are uneven.
-Actinides also show a greater multiplicity of oxidation states. Since in the lower actinides (first half of the actinide series ) the energy required for the conversion $5f\to 6d$ is less than that required for the conversion $4f\to 5d$, the lower actinides must show higher oxidation state such as $+$4, $+$5, $+$6 and $+$7.
-Similarly, since in the higher actinides( second half of the actinide series), the energy required for the conversion $5f\to 6d$ is more than that required for the conversion $4f\to 5d$ and the higher actinides should show lower oxidation states such as $+$2.

Therefore, the answer is an option (C). The most common oxidation state of actinides is $+$3.

Note: It should be noted that according to the definition the elements in which the extra electron enters 5f- orbitals of ${{(n-2)}^{th}}$ shell is known as actinides. But only the elements from Thorium (90) to Nobelium (102) fits into this definition. However, elements Actinium (89) and Lawrencium (103) are also considered as actinides since all these fifteen elements have similar physical and chemical properties.