Which of the following contains an 18-electron structure ?

Options

A. `Cu^(+)`
B. `Zn^(2+)`
C. `Hg^(2+)`
D. All of these

Explanation

To determine which of the given species contains an 18-electron structure, we need to analyze the electronic configurations of each species and count the electrons in their outermost shells.

### Step-by-Step Solution:

1. **Understand the 18-Electron Rule**:
The 18-electron rule states that a stable electron configuration for transition metals and their complexes often involves having a total of 18 electrons in the outermost shell. This includes the electrons in the s, p, and d orbitals.

2. **Identify the Options**:
The options given are:
- Copper (Cu⁺)
- Zinc (Zn²⁺)
- Mercury (Hg²⁺)
- All of the above

3. **Determine the Electronic Configuration**:
- **Copper (Cu)** has an atomic number of 29. Its electronic configuration is:
\[ \text{Cu: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^{10} \]
For Cu⁺ (removing one electron):
\[ \text{Cu}^+: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} \]
Counting the outermost electrons:
- 3s² (2) + 3p⁶ (6) + 3d¹⁰ (10) = 18 electrons.

- **Zinc (Zn)** has an atomic number of 30. Its electronic configuration is:
\[ \text{Zn: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} \]
For Zn²⁺ (removing two electrons):
\[ \text{Zn}^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} \]
Counting the outermost electrons:
- 3s² (2) + 3p⁶ (6) + 3d¹⁰ (10) = 18 electrons.

- **Mercury (Hg)** has an atomic number of 80. Its electronic configuration is:
\[ \text{Hg: } 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 4f^{14} 5d^{10} \]
For Hg²⁺ (removing two electrons):
\[ \text{Hg}^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 4f^{14} 5d^8 \]
Counting the outermost electrons:
- 5s² (2) + 5p⁶ (6) + 5d¹⁰ (10) = 18 electrons.

4. **Conclusion**:
All three species (Cu⁺, Zn²⁺, and Hg²⁺) have an 18-electron structure. Therefore, the correct answer is:
- **All of the above**.