Which reaction cannot give anhydrous `AlCl_(3)`:

Options

A. Passing dry `Cl_(2)` over heated aluminium powder
B. Heating a mixture of alumina and coke in a current of dry `Cl_(2)`.
C. Passing dry HCl over heated aluminium powder.
D. Heating of `AlCl_(3).6H_(2)O`

Explanation

To determine which reaction cannot give anhydrous AlCl₃, let's analyze each option step by step.

### Step 1: Analyze the reactions

1. **Passing dry Cl₂ over heated Aluminum powder**:
- Reaction: \( 2Al + 3Cl_2 \rightarrow 2AlCl_3 \)
- This reaction produces anhydrous AlCl₃.

2. **Heating a mixture of Alumina (Al₂O₃) and Coke in a current of dry Cl₂**:
- Reaction: \( Al_2O_3 + 3C + 3Cl_2 \rightarrow 2AlCl_3 + 3CO \)
- This reaction also produces anhydrous AlCl₃.

3. **Passing dry HCl over heated Aluminum powder**:
- Reaction: \( 2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2 \)
- This reaction produces anhydrous AlCl₃ as well.

4. **Dehydrating AlCl₃·6H₂O**:
- When AlCl₃·6H₂O is heated, it loses water of crystallization:
- \( AlCl_3·6H_2O \rightarrow AlCl_3 + 6H_2O \)
- However, AlCl₃ is a covalent compound and can react with any remaining water vapor to form aluminum hydroxide:
- \( AlCl_3 + 3H_2O \rightarrow Al(OH)_3 \)
- Therefore, this reaction does not yield anhydrous AlCl₃.

### Conclusion:
The reaction that cannot give anhydrous AlCl₃ is the **dehydration of AlCl₃·6H₂O**.

### Final Answer:
**Dehydration of AlCl₃·6H₂O cannot give anhydrous AlCl₃.**

---