Question

Which element from following has smallest ionic size in +3 state?

• A. Lu
• B. La
• C. Dy
• D. Nd

Hint:

For lanthanide +3 ions, size strictly follows atomic number. The higher the atomic number, the smaller the ionic radius. Order of size: $La^{3+} > Nd^{3+} > Dy^{3+} > Lu^{3+}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
All the given elements are Lanthanides (4f-series). In this series, as the atomic number increases, the atomic and ionic radii decrease. This phenomenon is known as "Lanthanide Contraction."

Step 2: Formula Application:
The order of elements in the series is: La (57) < Nd (60) < Dy (66) < Lu (71).

Step 3: Explanation:
Due to poor shielding by 4f electrons, the effective nuclear charge increases across the period, pulling the electron cloud closer to the nucleus. Since Lutetium (Lu) has the highest atomic number among the options, its $+3$ ion will be the smallest.

Step 4: Final Answer:
The smallest ion in the +3 state is Lu.