The colour of d-block elements is due to:

Options

A. nd-(n + 1)s transition
B. nd-(n + 1)p transition
C. nd-nd transition
D. nd-(n + 1)d transition.

Explanation

To answer the question regarding the color of d-block elements, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding d-block Elements**:
- d-block elements are transition metals found in groups 3 to 12 of the periodic table. They have partially filled d-orbitals.

2. **Role of d-orbitals**:
- The d-orbitals can split into different energy levels when in the presence of ligands (surrounding atoms or molecules). This phenomenon is known as crystal field splitting.

3. **Crystal Field Splitting**:
- In an octahedral field, the five d-orbitals split into two sets:
- The lower energy set (t2g)
- The higher energy set (eg)
- This splitting occurs due to the electrostatic interactions between the d-electrons and the surrounding ligands.

4. **Electron Transitions**:
- When electrons in the lower energy t2g orbitals absorb energy, they can be excited to the higher energy eg orbitals. This transition is what leads to the absorption of specific wavelengths of light.

5. **Visible Light and Color**:
- The energy difference between the split d-orbitals corresponds to certain wavelengths of light. When an electron transitions from t2g to eg (or vice versa), it can absorb light in the visible spectrum.
- The color observed in a compound is due to the wavelengths of light that are not absorbed but transmitted or reflected. The absorbed light gives rise to the complementary color.

6. **Conclusion**:
- The color of d-block elements is primarily due to the d-d transitions, where electrons move between the split d-orbitals. Therefore, the correct answer to the question is that the color of d-block elements is due to d-d transitions.

### Final Answer:
The color of d-block elements is due to d-d transitions.

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