Question

How many out of ${\left[Ti{F}_6\right]}^{2-},{\left[Co{F}_6\right]}^{3+},C{u}_{2}C{l}_2$ and ${\left[NiC{l}_4\right]}^{2-}$ are colourless?

Answer 1

Answer: 2

In ${\left[Ti{F}_6\right]}^{2-},T{i}^{4+}:3d^0$, colourless; as there is no unpaired electron.
In ${\left[Co{F}_6\right]}^{3-},C{o}^{3+}:3d^6$, coloured; as there are $4$ unpaired electrons.
In $C{u}_{2}C{l}_2,C{u}^{+}:3d^{10}$, colourless; as there is no unpaired electron.
In ${\left[NiC{l}_4\right]}^{2-},N{i}^{2+}:3d^8$, coloured; as there are $2$ unpaired electrons.
Thus, among the given, two species viz. ${\left[Ti{F}_6\right]}^{2-}$ and $C{u}_{2}C{l}_2$ are colourless.