Which of the following complex ions is expected to absorb visible...

Key Idea Only those transition metal complexes are expected to absorb visible light, in which d-subshell is incomplete (ie, has unpaired electron) and excitation of electron from a lower energy arbital to higher energy orbital is possible. (a) In $\left[\mathrm{Sc}\left(\mathrm{H}_2 \mathrm{O}\right)_3\left(\mathrm{NH}_3\right)_3\right]^{3+}, \mathrm{Sc}$ is present as $\mathrm{Sc}^{3+}$. $\mathrm{Sc}^{3+}=[\mathrm{Ar}]3 \mathrm{ d}^0, 4 \mathrm{ s}^0 Since,$ in $this complex excitation of electron is not possible, it will not absorb visible light. (b) In \left[\mathrm{Ti}(\mathrm{en})_2\left(\mathrm{NH}_3\right)_2\right]^{4+}, \mathrm{Ti}$ is present as $\mathrm{Ti}^{4+}$. $\mathrm{Ti}^{4+}=[\mathrm{Ar}]3 \mathrm{ d}^0, 4 \mathrm{ s}^0 Hence, it will not absorb visible light. (c)$ In \left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}, \mathrm{Cr}$is present as$\mathrm{Cr}^{3+}$.$\mathrm{Cr}^{3+}=[\mathrm{Ar}]3 \mathrm{ d}^3, 4 \mathrm{ s}^0 $<img src="/api/proxy-image?url=httpsSince, this complex has three unpaired electrons, excitation of$electrons is possible and thus, it is expected that this complex will absorb visible light. (d) In \left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}, \mathrm{Zn}$is present as$\mathrm{Zn}^{2+}$.$\begin{gathered}\mathrm{Zn}^{2+}=[\mathrm{Ar}]3 \mathrm{ d}^{10},4 \mathrm{ s}^0 \\ {\left[\mathrm{Zn}\left(\mathrm{NH}_{3}\right)_6\right]^{2+}=[\mathrm{Ar}]3 d^{10}} \end{gathered}
Hence, this complex will not absorb visible light.