Question

The point of dissimilarity between lanthanides and actinides is :
A. three outermost shells are partially filled
B. they show oxidation of $+ 3$ (common)
C. they are called inner transition elements
D. they are radioactive in nature

Answer 1

We know that the atomic number of lanthanides are from $58$ to $71$. They are the rare earth metals of the modern periodic table. Actinides are the elements whose atomic number varies from $90$ to $103$.

Complete step by step answer:
As we know that the actinides and the lanthanides constitutes the
f-block of the modern periodic table. The actinides and the lanthanides have valence electrons in their f orbital. These f block elements are also known as inner transition elements. Both lanthanides and actinides exhibit the $+ 3$ oxidation state . The common electronic configuration of lanthanides is $[Xe]4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$and the common electronic configuration of the actinides is $[Rn]5{f^{1 - 14}}6{d^{0 - 1}}7{s^2}$. Actinides are formed artificially by nuclear reactions . All the actinide elements are radioactive in nature. But in the lanthanide series only Promethium is radioactive ,rest of the lanthanide series elements are not radioactive . From the above discussion and explanation it is clear to us that the lanthanides and actinides have two outermost shells that are partially filled, they show oxidation of $+ 3$(common), they are called the inner transition elements and only actinides are radioactive .

Hence the correct option is D. they are radioactive in nature.

Additional information:
Actinides are very useful because of its radioactive nature. It is used in cardiac pacemakers. Uranium and plutonium of the actinide series are used in nuclear weapons and nuclear plants. Lanthanides are used to manufacture alloys to impart hardness and strength to metals.

Note:
Always remember that the lanthanides and actinides are called the inner transition elements of the modern periodic table. The electronic configuration of the lanthanides is $[Xe]4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$and the actinides have an electronic configuration of $[Rn]5{f^{1 - 14}}6{d^{0 - 1}}7{s^2}$. All the actinides elements are radioactive in nature but all lanthanides are not radioactive in nature , only Promethium of the lanthanide series is radioactive.