Question

The Lanthanoid ion which would form coloured compounds is ------------.
Atomic numbers: Yb = 70, Lu = 71, Pr = 59, La = 57

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

Hint:

When studying lanthanide ions, remember that the presence of partially filled 4f orbitals is key to forming coloured compounds. Ions with fully filled or empty f orbitals tend to be colourless.

Answer 1

The Correct Option is D

The lanthanide ions exhibit characteristic colours depending on their electronic configuration. Among the lanthanide ions, the colour of the compound typically arises due to the presence of partially filled 4f orbitals which allow electronic transitions. - Yb\(^{2+}\) and La\(^{3+}\) are not commonly known to form coloured compounds as their 4f orbitals are either completely filled or empty. - Lu\(^{3+}\) is relatively colourless as well because its 4f orbitals are empty in the ion. - Pr\(^{3+}\), however, has partially filled 4f orbitals and is known to form coloured compounds due to the electronic transitions in these orbitals.

Thus, the lanthanoid ion that forms coloured compounds is Pr\(^{3+}\).