Question

The atomic radii of Zr and Hf are almost identical. This is because of ________.

• A. change in effective atomic number
• B. lanthanoid contraction
• C. actinoid contraction
• D. usual nature of transition metals

Hint:

Lanthanoid contraction causes the atomic radii of the 2nd and 3rd transition series to be nearly the same.

Answer 1

The Correct Option is B

Step 1: Concept
Comparison of size in 4d and 5d transition series.
Step 2: Analysis
Zirconium (Zr) is a 4d element, and Hafnium (Hf) is a 5d element. Normally, size increases down a group, but between the 4d and 5d series, the 14 lanthanoid elements (filling of 4f orbitals) intervene.
Step 3: Reason
Poor shielding by 4f electrons causes the nucleus to pull the outer electrons more strongly, a phenomenon known as lanthanoid contraction. This compensates for the expected increase in size due to the extra shell.
Step 4: Conclusion
Hence, Zr and Hf have identical radii due to lanthanoid contraction.
Final Answer:(B)