The metal which can form cation having metal - metal bond

Options

A. Mercury
B. Copper
C. Osmium
D. Iron

Answer

To solve the question "The metal which can form cation having metal-metal bond," we need to analyze the options given: mercury, copper, osmium, and iron.

### Step-by-Step Solution:

1. **Understanding Cations and Metal-Metal Bonds**:
- A cation is a positively charged ion. In this case, we are looking for a cation that has a metal-metal bond, which implies that two metal atoms are bonded together in the cation.

2. **Identifying the Metals**:
- The metals listed are:
- A) Mercury (Hg)
- B) Copper (Cu)
- C) Osmium (Os)
- D) Iron (Fe)

3. **Analyzing Each Metal**:
- **Mercury (Hg)**:
- Mercury can form a cation known as the mercurous ion, \( \text{Hg}_2^{2+} \). In this ion, two mercury atoms are bonded together, forming a metal-metal bond. This is a classic example of a polyketion.
- **Copper (Cu)**:
- Copper typically forms monovalent (\( \text{Cu}^+ \)) and divalent (\( \text{Cu}^{2+} \)) cations but does not form a metal-metal bond in its cationic state.
- **Osmium (Os)**:
- Osmium can form various oxidation states but does not form a cation with a metal-metal bond.
- **Iron (Fe)**:
- Iron primarily forms \( \text{Fe}^{2+} \) and \( \text{Fe}^{3+} \) cations, which do not involve metal-metal bonding.

4. **Conclusion**:
- The only metal that can form a cation with a metal-metal bond is **Mercury (Hg)**, specifically in the form of the mercurous ion \( \text{Hg}_2^{2+} \).

### Final Answer:
- The correct option is **A) Mercury**.