The color of transition metal complexes is due to transition of electrons between:

Explanation

The color of transition metal complexes is due to the transition of electrons between different energy levels within the d orbitals of the metal ion. The d orbitals have different energy levels and can accommodate a varying number of electrons. When a transition metal ion forms a complex with ligands (atoms, ions, or molecules that surround the metal ion), the d orbitals split into different energy levels due to the influence of the ligands. This splitting is known as crystal field splitting. The energy difference between these split d orbitals corresponds to the energy of visible light. When white light passes through a colored solution containing transition metal complexes, certain wavelengths of light are absorbed by the electrons in the d orbitals, causing them to transition from a lower energy level to a higher energy level. The absorbed wavelengths are subtracted from the white light, resulting in the complementary color being observed. The specific color observed depends on the energy difference between the split d orbitals, which is influenced by factors such as the nature of the ligands and the oxidation state of the metal ion. Different ligands can induce different degrees of splitting, leading to variations in color. For example, complexes with ligands that create larger energy differences between the d orbitals tend to absorb longer wavelengths (lower energy) of light and appear yellow or red. Conversely, complexes with ligands that create smaller energy differences tend to absorb shorter wavelengths (higher energy) of light and appear blue or green. Overall, the absorption of specific wavelengths of light by transition metal complexes due to electron transitions within the d orbitals is responsible for their characteristic colors. When transition metals form complex ions or compounds, the d orbitals split into two energy levels. Electrons from the lower energy level absorb light of wavelength corresponding to the visible region in the EM spectrum and get excited to a higher energy level. The remaining unabsorbed wavelength is reflected and that gives the characteristic colour to the complex. As the energy difference between the high and lower energy levels of electrons varies for different complexes, the colour also varies. As discussed, the splitting occurs in d-orbital and transition of electrons between the two energy levels (d-d transition) is responsible for imparting different colours. Therefore option B is correct. (Source: PCTB book 2, page 102)