Question

Which of the following lanthanide ions do not exhibit color?

• A. $L{u}^{+3}$ and $L{a}^{+3}$
• B. $L{u}^{+2}$ and $L{a}^{+2}$
• C. $C{e}^{+3}$ and $C{e}^{+4}$
• D. $P{r}^{+3}$ and $C{e}^{+3}$

Answer 1

The correct option is A $L{u}^{+3}$ and $L{a}^{+3}$

Many trivalent lanthanide ions are colored both in the solid state and in aqueous state due to incomplete filling of f-orbitals.
$L{u}^{+3}$ and $L{a}^{+3}$don’t exhibit color due to absence of unpaired electrons. All trivalent lanthanide ions except $L{a}^{+3}$ and $L{u}^{+3}$ are paramagnetic due to presence of unpaired electrons.

$C{e}^{+3},L{u}^{2+}$ and $P{r}^{3+}$ has unpaired electrons so they will exhibit colour.