alleryEu²⁺ is more stable than other Ln²⁺ because:
AEu(II) achieves stable half-filled 4f⁷ configuration
BAlways
CRandom
DLight
Answer & Solution
Correct answer: A. Eu(II) achieves stable half-filled 4f⁷ configuration
Eu²⁺: 4f⁷ (half-filled, stable by Hund's rule).
Yb²⁺: 4f¹⁴ (full, also stable).
Both are reasonably stable in solution (unlike most Ln²⁺ which are strong reducers).
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