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Q.
The colour of the transition metal ions is due to
NTA AbhyasNTA Abhyas 2020The d-and f-Block Elements
Solution:
The colour of transition metal ions is due to $\text{d-d}$ transition. When a ligand approaches metal ion, its $\text{d}$ -orbital does not remains degenerate.
They split into two sets, one consisting of lower energy and the other consisting higher energy level.
Thus electrons can jump from lower energy $\text{d}$ -orbitals to higher energy $\text{d}$ -orbitals. Such transition are known as $\text{d-d}$ transition.
The required amount of energy during $\text{d-d}$ transition is obtained by absorption of light of a particular wavelength in the region of visible light.
Note: Sometimes the colour of transition metal ions is also due to charge transfer spectra.