Question

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

• A. Pr
• B. Sm
• C. La
• D. Yb

Hint:

Think of lanthanoid contraction: ionic size decreases steadily as atomic number increases.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Along the lanthanoid series the \(4f\) electrons shield the nuclear charge poorly, so the size of \(\text{Ln}^{3+}\) ions decreases with increasing atomic number. This is called lanthanoid contraction.

Step 2: Apply to the elements
The atomic numbers are La 57, Pr 59, Sm 62 and Yb 70.

Step 3: Conclusion
La has the lowest atomic number, so \(\text{La}^{3+}\) is the largest ion and \(\text{Yb}^{3+}\) is the smallest.

Final Answer:
\(\text{La}^{3+}\) has the largest ionic size. \[ \boxed{\text{(C) }\text{La}} \]