alleryStart learning →La is [Xe] 6s2 5d1 and not 6s2 4f1 because
A5d is slightly lower than 4f
B6s is empty in lanthanum
C4f orbitals do not exist
DLa has no valence electrons
Answer & Solution
Correct answer: A. 5d is slightly lower than 4f
For lanthanum the 4f level lies slightly above 5d, so the extra electron enters 5d.
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