Question

Knowing that the chemistry of lanthanids (Ln) is dominated by its +3 oxidation state, which of the following statements are correct?
(I) The ionic sized of Ln (III) decreases in general with increasing atomic number.
(II) Ln (III) compounds are generally colourless.
(III) Ln (III) hydroxides are mainly basic in character.
(IV) Because of the large size of the Ln (III) ions, the bonding in its compounds is predominently ionic in character.

• A. I, III and III
• B. II, III and IV
• C. I, II and IV
• D. I, III and IV

Answer 1

The correct option is D I, III and IV

The ionic radii of trivalent lanthanides steadily decreases with increase in atomic number due to lanthanide contraction.
In lanthanides (At no. of elements 58 to 71) the electronic configuration of three outermost shelts are $(n-2{)}^{f-14},(n-1)s^2{p}^6{d}^{10-1}n{s}^2$.
So, most of the trivalent lanthanoid compounds except that of $L{a}^{+3}$ and $L{u}^{+3}$ are coloured, both in the solid state and in the aqueous solution. These ions are coloured due to the presence of unpaired f-electrons.
Due to small electronegativity and large size of the Ln (III) ions the bonding in its compounds is predominently ionic in character.