Which of the following complex ions is expected to absorb visible light ? (At no. $\mathrm{Zn}=30,…

Which of the following complex ions is expected to absorb visible light ? (At no. $\mathrm{Zn}=30, \mathrm{Sc}=21, \mathrm{Ti}=22, \mathrm{Cr}=24$ )
  1. $\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_6\right]^{2+}$
  2. $\left[\mathrm{Sc}\left(\mathrm{H}_2 \mathrm{O}\right)_3\left(\mathrm{NH}_3\right)_3\right]^{3+}$
  3. $\left[\mathrm{Ti}(\mathrm{en})_2\left(\mathrm{NH}_3\right)_2\right]^{4+}$
  4. $\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_6\right]^{3+}$

Solution

$\mathrm{Cr}^{3+} \rightarrow \mathrm{Is}^2, 2 \mathrm{~s}^2 2 \mathrm{p}^6, 3 \mathrm{~s}^2 3 \mathrm{p}^6 3 \mathrm{~d}^3$ Unpaired electron shows colour so absorb visible light.

Asked in: NEET 2009 (Mains)

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