Question

The lanthanide that would show colour is:

• A. $G{d}^{3+}$
• B. $L{a}^{3+}$
• C. $L{u}^{3+}$
• D. $S{m}^{3+}$

Answer 1

The correct option is D $S{m}^{3+}$

The electronic configuration of $G{d}^{3+}$ is $\left[Xe\right]4f^7$

The electronic configuration of $L{a}^{3+}$ is $\left[Xe\right]4f^0$

The electronic configuration of $L{u}^{3+}$ is $\left[Xe\right]4f^{14}$

The electronic configuration of $S{m}^{3+}$ is $\left[Xe\right]4f^5$

Only $S{m}^{3+}$ among the given options does possess any half-filled or fully filled $4f$ orbital, hence only $S{m}^{3+}$ would show colour.