, , and have ionic radii in the increasing order as

Question

, ,  and  have ionic radii in the increasing order as

Canvas Classes · Accepted Answer

Strategy:
 Apply the principle of "Lanthanoid Contraction". In the  series, the poor shielding effect of -electrons means the effective nuclear charge increases steadily, causing a progressive decrease in ionic radius.

Step 1: Locate elements in the lanthanide series
-  group, Period 6: Lanthanum ().
- Cerium ().
- Promethium ().
- Ytterbium ().

Step 2: Apply the contraction trend
Radius order: .

Step 3: Determine increasing order

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