What condition must typically be met for a transition metal ion to produce color via d-d transitions?

Answer

It must possess at least one electron and at least one empty d orbital ($d^1$ through $d^9$)

For an electron to jump between split d orbitals upon absorbing visible light, there must be an electron available to be promoted and an empty orbital available at a higher energy level.

What condition must typically be met for a transition metal ion to produce color via d-d transitions?

#Videos

Why do Transition Metals Form Coloured Compounds? - YouTube

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