Out of $\mathrm{TiF}_6^{2-}$ and $\mathrm{CoF}_6^{3-}, \mathrm{Cu}_2 \mathrm{Cl}_2$ and $\mathrm{NiCl}_4^{2-}$ ( $\mathrm{Z}$ of $\mathrm{Ti}=22, \mathrm{Co}=27, \mathrm{Cu}=29, \mathrm{Ni}=28)$ the colourless species are :

• A

  $\mathrm{CoF}_6^{3-}$ and $\mathrm{NiCl}_4^{2-}$
• B

  $\mathrm{TiF}_6^{2-}$ and $\mathrm{CoF}_6^{3-}$
• C

  $\mathrm{Cu}_2 \mathrm{Cl}_2$ and $\mathrm{NiCl}_4^{2-}$
• Correct answer
  D

  $\mathrm{TiF}_6^{2-}$ and $\mathrm{Cu}_2 \mathrm{Cl}_2$

Hence, the correct answer is option: 'D'.