Mercury is a liquid metal because

Options

A. it has a completely filled d-orbital that prevents d-d overlapping of orbitals
B. it has a completely filled d-orbital that causes d-d overlapping
C. it has a completely filled s-orbital
D. it has a small atomic size.

Answer

**Step-by-Step Solution:**

1. **Understanding Mercury's State:**
- Mercury (Hg) is unique among metals as it exists in a liquid state at room temperature. This property is attributed to its electronic configuration and the nature of its atomic orbitals.

2. **Electronic Configuration of Mercury:**
- The electronic configuration of mercury is given as:
\[ \text{Hg: } [Xe] 4f^{14} 5d^{10} 6s^{2} \]
- This indicates that mercury has a completely filled 4f and 5d subshells, as well as a filled 6s subshell.

3. **Role of the 6s Orbital:**
- The completely filled 6s orbital is significant because it is stable and close to the nucleus. This stability prevents the 6s electrons from participating in bonding with other elements.

4. **Screening Effect of the f-Orbitals:**
- The f-orbitals (4f in this case) poorly screen the nuclear charge. This means that the effective nuclear charge felt by the outermost electrons (in the 6s orbital) is relatively high, which stabilizes these electrons and keeps them from being involved in bonding.

5. **Lack of Bond Formation:**
- Due to the stability of the filled 6s orbital and the poor screening effect of the f-orbitals, mercury does not form metallic bonds like other solid metals. This inability to bond leads to its liquid state at room temperature.

6. **Conclusion:**
- Therefore, the correct answer to the question "Why is mercury a liquid metal?" is that it has a completely filled 6s orbital, which prevents it from forming bonds with other elements, thus allowing it to remain in a liquid state.

**Final Answer:**
Mercury is a liquid metal because it has a completely filled 6s orbital, preventing it from forming bonds with other elements.

---