Question

Which of the following lanthanide ion is coloured?}

• A. \(La^{3+}\)
• B. \(Lu^{3+}\)
• C. \(Gd^{3+}\)
• D. \(Sm^{3+}\)
• E. \(Yb^{2+}\)

Hint:

Lanthanide ions are coloured mainly due to \(f\)-\(f\) transitions. Empty and fully filled \(f\)-subshell ions are usually colourless.

Answer 1

The Correct Option is D

Lanthanide ions are coloured when they have partially filled \(4f\)-orbitals. Check:

• \(La^{3+}\): \(4f^0\), colourless
• \(Lu^{3+}\): \(4f^{14}\), colourless
• \(Gd^{3+}\): \(4f^7\), weak but often treated specially
• \(Sm^{3+}\): partially filled \(4f\), coloured

Thus the clearly coloured ion among the options is: \[ \boxed{Sm^{3+}} \]
Hence, the correct answer is: \[ \boxed{(D)} \]