Question

The UV-visible absorption bands in the spectra of lanthanoid ions are ‘X’, probably because of the excitation of electrons involving ‘Y’. The ‘X’ and ‘Y’, respectively, are :

• A. Broad and f orbitals
• B. Narrow and f orbitals
• C. Broad and d and f orbitals
• D. Narrow and d and f orbitals

Answer 1

Answer: (B)

Narrow and f orbitals

Answer 2

Lanthanides have narrow absorption bands in the UV-visible region of the spectrum. This is because the f orbitals are shielded effectively by the outer electrons, so the electronic transitions within the $f$ orbitals are less affected by the external environment (ligands or other ions). This shielding leads to narrow and well-defined absorption bands. The transitions responsible for these absorptions involve $f$ orbitals.