Outof $\left[\mathrm{TiF}_{6}ight]^{2-},\left[\mathrm{CoF}_{6}ight]^{3-}, \mathrm{Cu}_{2} \mathrm{Cl}_{2}$…

Outof $\left[\mathrm{TiF}_{6}ight]^{2-},\left[\mathrm{CoF}_{6}ight]^{3-}, \mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and $\left[\mathrm{NiCl}_{4}ight]^{2-}$ $(Z$ of $T i=22, C o=27, C u=29, N i=28)$, the colourless species are:
  1. $\mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and $\left[\mathrm{NiCl}_{4}ight]^{2-}$
  2. $\left[\mathrm{TiF}_{6}ight]^{2-}$ and $\mathrm{Cu}_{2} \mathrm{Cl}_{2}$
  3. $\left[\mathrm{CoF}_{6}ight]^{3-}$ and $\left[\mathrm{NiCl}_{4}ight]^{2-}$
  4. $\left[\mathrm{TiF}_{6}ight]^{2-}$ and $\left[\mathrm{CoF}_{6}ight]^{3-}$

Solution

The colour exhibited by transition metal ions is due to the presence of unpaired electrons in $d$ -orbitals which permits the $d-d$ excitation of electrons.
In $\left[\mathrm{TiF}_{6}ight]^{2-}-\mathrm{Ti}$ is in $+4$ O.S. $; 3 d^{0}$ -colourless
In $\left[\mathrm{CoF}_{6}ight]^{3-}-\mathrm{Co}$ is in $+3 \mathrm{O} \cdot \mathrm{S} ; 3 d^{5}-$ coloured
In $\mathrm{Cu}_{2} \mathrm{Cl}_{2}-\mathrm{Cu}$ is in $+1$ O.S. $; 3 d^{10}-$ colourless
In $\left[\mathrm{NiCl}_{4}ight]^{2-}-\mathrm{Ni}$ is in $+2 \mathrm{O} \cdot \mathrm{S} ; 3 d^{8}-$ coloured

Asked in: JEE-TOPICTESTS-CHEMISTRY

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