Chemistry - Complete d-block Question with Solution | TestHub

Key Idea Species without unpaired electrons are colourless because transition of electron is not passible. (a) In ${\mathrm{TiF}}_6^{2-},\mathrm{Ti}$ is present as ${\mathrm{Ti}}^{4+}$. $${\mathrm{Ti}}^{4+}=[\mathrm{Ar}]3{\mathrm{d}}^{0}4{\mathrm{s}}^0$$ Hence, ${\mathrm{TiF}}_6^{2-}$ is colourless. (b) In ${\mathrm{CoF}}_6^{3-}$, Co is present as ${\mathrm{Co}}^{3+}$
Due to presence of unpaired electrons, ${\mathrm{CoF}}_6^{3-}$ is coloured. (c) In ${\mathrm{Cu}}_2{\mathrm{Cl}}_2,\mathrm{Cu}$ is present as ${\mathrm{Cu}}^{+}$.
Due to absence of unpaired electron, ${\mathrm{Cu}}_2{\mathrm{Cl}}_2$ is colourless. (d) In ${\mathrm{NiCl}}_4^{2-},\mathrm{Ni}$ is present as ${\mathrm{Ni}}^{2+}$.
Since, unpaired electrons are present, ${\mathrm{NiCl}}_4^{2-}$ is coloured. Hence, ${\mathrm{TiF}}_6^{2-}$ and ${\mathrm{Cu}}_2{\mathrm{Cl}}_2$ are colourless species.