The dand fblock elements - Result Question 20
####20. Out of $TiF_6^{2-}, CoF_6^{3-}, Cu_2 Cl_2$ and $NiCl_4^{2-}$ ( $Z$ of $Ti=22, Co=27, Cu=29, Ni=28)$, the colourless species are:
[2009]
(a) $Cu_2 Cl_2$ and $NiCl_4^{2-}$
(b) $TiF_6^{2-}$ and $Cu_2 Cl_2$
(c) $CoF_6^{3-}$ and $NiCl_4^{2-}$
(d) $TiF_6^{2-}:$ and $CoF_6^{3-}$
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Solution:
- (b) In $TiF_6^{2-}-Ti$ is in +4 O.S. $; 3 d^{0}=$ colourless
In $CoF_6^{3-}-Co$ is in +3 O.S $; 3 d^{5}=$ coloured
In $Cu_2 Cl_2-Cu$ is in +1 O.S. $; 3 d^{10}-$ colourless
In $NiCl_4^{2-}-Ni$ is in $+2 O . S ; 3 d^{8}$ - coloured
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.
