Question

The colour of $Cr{O}_4^{2-}$ is due to
a.) Charge transfer
b.) d-d transition
c.) it does not show colour
d.) none of above

Answer 1

Hint: A compound is colour by the nature of charge transfer. Moreover the large metal iron and their salts are hued because of the essence of unpaired electrons in metal particles. The d-d transition where an electron jumps from one d orbital to another.

Complete step by step answer:
In$Cr{O}_4^{2-}$, Cr is in +6 oxidation state and has $d^0$ arrangement. The colour is because of charge transfer not because of d - d transition.
The term Charge transfer or we can say charge exchange, states that a cycle where a particle takes at least one electron from another atom. They range from planetary climates or atmosphere, the heliosphere, the interstellar medium and stars to worlds and bunches of cosmic systems, where charge move may even be observationally connected to dark matter. The electron transfer is a process by which an electron moves from one atom or molecule to another.
So, the correct answer is “Option A”.

d-d TRANSITION:
In a d–d transition, an electron in a d orbital on the metal is energized by a photon to another d orbital of higher energy. In edifices of the transition metals, the d orbitals don't all have a similar energy.

Note: The only reason behind why transition metals specifically are colourful is because they have unfilled or either half-filled d orbitals. There is a Crystal field hypothesis which clarifies the parting of the d orbital, which parts the d orbital to a higher and lower orbital. Presently, the electrons of the change metal can "jump".