NEET 2021 · ChemistryLanthanoidsPrevious Year Question
Zr (Z = 40) and Hf (Z = 72) have similar atomic and ionic radii because of:
Answer: (A) (a) lanthanoid contraction.. \textbf{Answer:} (a) lanthanoid contraction.
- A.(a) lanthanoid contraction.✓
- B.(b) having similar chemical properties.
- C.(c) belonging to same group.
- D.(d) diagonal relationship.
Correct Answer
(A) (a) lanthanoid contraction.
Solution & Explanation
\textbf{Answer:} (a) lanthanoid contraction. \textbf{Solution:} Zr (4d series) and Hf (5d series) lie in the same group. Normally the 5d element would be appreciably larger, but the 14 lanthanoids between La and Hf cause a steady decrease in size known as the lanthanoid contraction. This contraction almost exactly cancels the expected increase in size on going down the group, so Zr and Hf end up with nearly identical atomic and ionic radii. Hence option (a) is correct.
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