Question

Lanthanoid ions shows:

• A. Magnetic properties
• B. Colour and spectral properties
• C. Lanthanide contraction
• D. All of these

Answer 1

The correct option is D All of these

All lanthanide elements form trivalent cations, $L{n}^{3+}$. As there are seven 4f orbitals the number of unpaired electrons can be as high as 7 which gives rise to the colour spectrum and large magnetic moments observed for lanthanide compounds.
Neither $L{a}^{3+}$ nor $L{u}^{3+}$ ion shows any colour but the rest do so due to incomplete filling of f-orbitals.
The lanthanide contraction, the reduction in size of the $L{n}^{3+}$ ion from $L{a}^{3+}$(103 pm) - $L{u}^{3+}$(86.1 pm) is often explained by the poor shielding of 4f electrons.