Among the following, the coloured compound is

Among the following, the coloured compound is
  1. $\mathrm{CuCl}$
  2. $\mathrm{K}_3\left[\mathrm{Cu}(\mathrm{CN})_4\right]$
  3. $\mathrm{CuF}_2$
  4. $\left[\mathrm{Cu}\left(\mathrm{CH}_3 \mathrm{CN}_4\right)\right] \mathrm{BF}_4$

Solution

In $\mathrm{CuF}_2, \mathrm{Cu}^{2+}$ ions exist, having $d^9$-configuration. Unpaired electron causes colour ( $d-d$ transition) In the crystalline form, $\mathrm{CuF}_2$ is blue coloured

Asked in: JEE Advanced 2008 (Paper 2)

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