Which halogen cannot form `FeX_3 & FeX_2`

Options

A. I
B. Br
C. F
D. Cl

Answer

To determine which halogen cannot form \( \text{FeX}_3 \) and \( \text{FeX}_2 \), we need to analyze the stability of the iron halides formed with different halogens.

### Step-by-Step Solution:

1. **Understanding Iron Halides:**
- Iron can form two types of halides: \( \text{FeX}_2 \) (where iron is in the +2 oxidation state) and \( \text{FeX}_3 \) (where iron is in the +3 oxidation state).
- The halogens in question are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

2. **Analyzing the Halogens:**
- As we move down the group in the periodic table, the size of the halogen atoms increases, and their electronegativity decreases.
- This means that heavier halogens (like iodine) are less effective at stabilizing higher oxidation states due to their larger atomic size and lower electronegativity.

3. **Stability of Iron Iodide:**
- \( \text{FeI}_3 \) (iron(III) iodide) is known to be unstable. Iodine, being a larger atom, has a lower tendency to hold onto electrons and can act as a reducing agent.
- In the presence of iodine, \( \text{I}^- \) can easily reduce \( \text{Fe}^{3+} \) to \( \text{Fe}^{2+} \), thus favoring the formation of \( \text{FeI}_2 \) instead of \( \text{FeI}_3 \).

4. **Conclusion:**
- Since \( \text{FeI}_3 \) does not exist due to its instability and the reducing nature of iodine, we conclude that iodine is the halogen that cannot form \( \text{FeX}_3 \) and \( \text{FeX}_2 \).

### Final Answer:
The halogen that cannot form \( \text{FeX}_3 \) and \( \text{FeX}_2 \) is **Iodine (I)**.

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