The correct answer is (3) Due to d-d transition.
Transition elements form coloured ions due to d-d transition. The d-orbitals in transition metal ions are partially filled with electrons. When these ions absorb light, the electrons in the d-orbitals get excited to higher energy levels. This absorption of light falls in the visible region of the electromagnetic spectrum, leading to the appearance of specific colors.
The energy difference between the d orbitals corresponds to the energy of visible light, and the absorption of specific wavelengths results in the observed colors. The color seen is complementary to the absorbed color, as the absorbed color is subtracted from the white light, and the remaining color is observed.
For example, when a transition metal ion absorbs red light, it appears green or blue-green to the human eye since green/blue-green light is not absorbed, but rather reflected or transmitted. Similarly, when a transition metal ion absorbs yellow light, it appears purple to the human eye. The phenomenon of d-d transition is responsible for the beautiful and varied colors exhibited by transition metal ions in different chemical compounds and solutions. |
