In the formation of a Ce3+ ion from cerium (Ce), the electrons are removed from which orbitals?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 5d and 6s
When a lanthanoid atom forms a positive ion, electrons are removed first from the outermost 6s orbital, then from the 5d orbital if it holds an electron, and only then from the inner 4f orbitals.
Cerium (Z = 58) has the configuration:
Ce: [Xe] 4f1 5d1 6s2
\( \ce{Ce^{3+}} \): [Xe] 4f1
To form \( \ce{Ce^{3+}} \), three electrons are lost: the two 6s electrons and the one 5d electron. The 4f electron stays.
NCERT (2026-27 edition):
Electronic Configurations – …
