Question

Zn and Cd comlex are colourless

Answer 1

Some of the of the d-block elements are colorless in aqueous solution while others are not. This is due to splitting of the d-orbital. The reason they split is because of the electrostatic interactions between the electrons of the ligand and the lobes of the d-orbital.

In order for a compound or solution to exhibit color, the central atom of the compound should have at least an unpaired d electron in it. This will absorb light and then re-emit it at a particular wavelength thus giving it a distinctive color.

In other words, the colors of tradition elements compounds are due to d-d transition which is possible only when the subshell have unpaired electrons.

Even though Zinc and Cadmium are metals and and are elements of d-block family, showing a 2+ oxidation states that involves (n-1)d^10 configurations, they are not considered to be a part of Transition metals. They have no unpaired electrons in the subshell. Therefore, since they don’t have unpaired electrons, the d-d transition is not possible, so they don’t show any color.

I hope you find this answer helpful!!

Answer 2

Due to electrostatic interaction between electrons of the loves of d orbital there is splitting of the d orbital.Hence No unpaired electron in d orbital and does not exhibit colour and appear colourless