Anhydrous ferric chloride is prepared by:

Options

A. dissolving ferric hydroxide in dilute `HCl`
B. dissolving ferric hydroxide in concentrated `HCl`
C. by passing dry `Cl_(2)` gas over heated scrap iron
D. by dissolving iron(III) oxide in concentrated `HCl`.

Explanation

To prepare anhydrous ferric chloride (FeCl3), we can follow these steps:

### Step 1: Understand the Composition of Anhydrous Ferric Chloride
Anhydrous ferric chloride is the dry form of FeCl3, which means it does not contain any water molecules associated with it.

### Step 2: Analyze the Given Options
We have four options to consider:
1. Dissolving ferric hydroxide in dilute HCl
2. Dissolving ferric hydroxide in concentrated HCl
3. Passing Cl2 gas over heated scrap iron
4. Dissolving iron (III) oxide in concentrated HCl

### Step 3: Evaluate Each Option
- **Option 1**: Dissolving ferric hydroxide in dilute HCl will produce FeCl3·6H2O (hydrated form) because there is water present in dilute HCl.

- **Option 2**: Dissolving ferric hydroxide in concentrated HCl will also yield FeCl3·6H2O due to the presence of water in concentrated HCl.

- **Option 3**: Passing Cl2 gas over heated scrap iron will produce anhydrous ferric chloride (FeCl3) directly without any water.

- **Option 4**: Dissolving iron (III) oxide (Fe2O3) in concentrated HCl will also yield hydrated ferric chloride (FeCl3·6H2O) because of the water in concentrated HCl.

### Step 4: Conclusion
The only method that produces anhydrous ferric chloride is by passing Cl2 gas over heated scrap iron. Therefore, the correct answer is:

**Option 3: By passing Cl2 gas over heated scrap iron.**

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