Question

Which actinoid from following in its +3 state has largest size?

• A. U
• B. Bk
• C. Es
• D. Md

Hint:

In $f$-block series (both Lanthanoids and Actinoids), size decreases from left to right due to poor shielding by $f$-electrons.

Answer 1

The Correct Option is A

Step 1: Concept
Across the actinoid series, there is a steady decrease in the size of atoms or $M^{3+}$ ions with increasing atomic number. This is known as the actinoid contraction.

Step 2: Analysis
- The elements given are Uranium (92), Berkelium (97), Einsteinium (99), and Mendelevium (101). - Uranium has the lowest atomic number among the options.

Step 3: Conclusion
Since size decreases as the atomic number increases, the element with the lowest atomic number (Uranium) will have the largest size in its +3 state.
Final Answer: (A)