Which of the following iron salts exists as a dimer?

Options

A. Ferric chloride
B. Ferrous chloride
C. Ferrous sulphite
D. Mohr's salt

Answer

To determine which of the given iron salts exists as a dimer, we will analyze each option step by step.

### Step 1: Identify the Iron Salts
The options provided are:
- A: FeCl3 (Ferric Chloride)
- B: FeSO4 (Ferrous Sulfate)
- C: FeCl2 (Ferrous Chloride)
- D: Mohr's Salt (FeSO4·(NH4)2SO4·6H2O)

### Step 2: Analyze Each Salt
1. **FeCl3 (Ferric Chloride)**:
- Ferric chloride can exist as a dimer in the vapor phase. In the dimerized form, it is represented as Fe2Cl6. This occurs due to the low melting and boiling points of FeCl3, which leads to the formation of dimers in the vapor state.

2. **FeSO4 (Ferrous Sulfate)**:
- Ferrous sulfate does not exist as a dimer. It typically exists in a monomeric form in solution.

3. **FeCl2 (Ferrous Chloride)**:
- Ferrous chloride also does not form dimers. It exists in a monomeric form.

4. **Mohr's Salt (FeSO4·(NH4)2SO4·6H2O)**:
- Mohr's salt is a double salt and does not exist as a dimer. It remains in its ionic form in solution.

### Step 3: Conclusion
From the analysis:
- The only iron salt that exists as a dimer is **FeCl3** (Ferric Chloride), which forms Fe2Cl6 in the vapor phase.

### Final Answer
**FeCl3 (Ferric Chloride) exists as a dimer.**

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