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 need to analyze the electronic configurations of Zinc (Zn) and Mercury (Hg) and understand the reasons behind the lack of color in their ions.

### Step-by-Step Solution:

1. **Identify the Elements**:
- Zinc (Zn) and Mercury (Hg) are both transition metals located in Group 12 of the periodic table.

2. **Write the Electronic Configurations**:
- For Zinc (Zn):
- Atomic number = 30
- Electronic configuration = [Ar] 3d^10 4s^2
- For Mercury (Hg):
- Atomic number = 80
- Electronic configuration = [Xe] 4f^14 5d^10 6s^2

3. **Analyze the d-Orbitals**:
- In both Zn and Hg, the d-orbitals are completely filled:
- Zn has a filled 3d^10 subshell.
- Hg has a filled 4f^14 and 5d^10 subshells.
- A fully filled d-orbital means there are no unpaired electrons available for transitions.

4. **Understand the Color of Ions**:
- Transition metals typically form colored ions due to the presence of unpaired d-electrons. When light hits these ions, electrons can be excited from a lower energy d-orbital to a higher energy d-orbital, resulting in the absorption of specific wavelengths of light and the appearance of color.
- Since both Zn and Hg have completely filled d-orbitals, they do not have unpaired electrons to undergo such electronic transitions.

5. **Evaluate the 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)

6. **Conclusion**:
- The correct reason why Zn and Hg do not form colored ions is that their inner d-orbitals are completely filled, preventing any electronic transitions that would lead to color.

### Final Answer:
Zn and Hg do not form colored ions because their inner d-orbitals are completely filled.