Question

Which of the following complex ions is expected to absorb visible light?

(At number Zn = 30, Sc = 21, Ti = 22, Cr = 24)

• A. $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$
• B. $\left[Sc\right(H_{2}O{)}_3(N{H}_3{)}_3{]}^{3+}$
• C. $\left[Ti\right(en{)}_2(N{H}_3{)}_2{]}^{4+}$
• D. $\left[Cr\right(N{H}_3{)}_6{]}^{3+}$

Answer 1

The correct option is D

$\left[Cr\right(N{H}_3{)}_6{]}^{3+}$

In $Z{n}^{2+}$, the $t_{2g}$ and $e_g$ orbitals are completely filled $\Rightarrow$ no transition $\Rightarrow$ no absorption of visible light. Similarly, $S{c}^{3+}$ and $T{i}^{4+}$ do not have any d electrons, there are no transitions.

In case of $C{r}^{3+}\Rightarrow 3d^3\Rightarrow$ transition will take place.