The correct order of atomic radii is:

Question

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Strategy:
 Lanthanoid atomic radii generally decrease from left to right due to "Lanthanoid Contraction". However, elements like Europium () show anomalies based on their stable half-filled  configuration.

Step 1: Evaluate the lanthanide members
- Atomic numbers:  (58),  (63),  (67).
- Due to its half-filled  subshell, Europium () acts as a divalent metal in the solid state, giving it an anomalously larger atomic radius compared to its neighbors.
- Between  and , the radius decreases due to con

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