Zn and Hg do not forms coloured ions because

Options

A. They are soft
B. Their innerd-orbitals are completely filled
C. They have only 2-electrons in the outer most shell
D. None of these

Answer

To answer the question "Zn and Hg do not form coloured ions because:", we will analyze the electronic configurations of zinc (Zn) and mercury (Hg) and understand the reasons behind their inability to form colored ions.

### Step-by-Step Solution:

1. **Identify the Atomic Numbers and Electronic Configurations**:
- **Zinc (Zn)**: Atomic number is 30.
- Electronic configuration: \( \text{[Ar]} 3d^{10} 4s^2 \)
- **Mercury (Hg)**: Atomic number is 80.
- Electronic configuration: \( \text{[Xe]} 4f^{14} 5d^{10} 6s^2 \)

2. **Analyze the d-Orbitals**:
- For **Zinc**:
- The 3d subshell is completely filled with 10 electrons (\(3d^{10}\)).
- There are no unpaired electrons in the 3d subshell.
- For **Mercury**:
- The 5d subshell is also completely filled with 10 electrons (\(5d^{10}\)).
- Similarly, there are no unpaired electrons in the 5d subshell.

3. **Understand the Concept of Color in Ions**:
- Transition metal ions typically exhibit color due to the presence of unpaired electrons in their d-orbitals. When light hits these ions, electrons can be excited from a lower energy d-orbital to a higher energy d-orbital (d-d transition), which results in the absorption of specific wavelengths of light and the appearance of color.

4. **Conclusion**:
- Since both zinc and mercury have completely filled d-orbitals with no unpaired electrons, they cannot undergo d-d transitions. Therefore, they do not form colored ions.

5. **Select the Correct Reason**:
- Among the provided options:
- Option 1: They are soft (Incorrect)
- Option 2: Their inner d-orbitals are completely filled (Correct)
- Option 3: They have only two electrons in the outermost shell (Incorrect)
- Option 4: None of these (Incorrect)
- The correct answer is **Option 2**: Their inner d-orbitals are completely filled.

### Final Answer:
Zn and Hg do not form colored ions because their inner d-orbitals are completely filled, resulting in no unpaired electrons available for d-d transitions.

---