Question

Which among the following lanthanoids has the smallest atomic size?

• A. Pr
• B. Ce
• C. Sm
• D. Pm

Hint:

In the lanthanoid series, atomic size decreases as the atomic number increases due to the increasing nuclear charge.

Answer 1

The Correct Option is C

Step 1: Understanding lanthanoid atomic sizes.
In the lanthanoid series, the atomic size generally decreases as the atomic number increases due to the increasing nuclear charge and the similar electron configuration. The smallest atomic size is found in Sm (Samarium).

Step 2: Analyzing the options.
(A) Pr: This element has a relatively larger atomic size compared to Sm.
(B) Ce: This element also has a larger atomic size compared to Sm.
(C) Sm: Correct — Sm has the smallest atomic size among the lanthanoids.
(D) Pm: This element has a larger atomic size than Sm.

Step 3: Conclusion.
The correct answer is (C) Sm, as it has the smallest atomic size among the lanthanoids.