Most covalent halide of aluminium is

Options

A. `AlI_3 `
B. `AlBr_3 `
C. `AlCl_3 `
D. `AlF_3 `

Answer

To determine the most covalent halide of aluminum, we will analyze the halides of aluminum: AlI3, AlBr3, AlCl3, and AlF3. We will apply Fajans' rules, which help us understand the covalent and ionic character of compounds based on the size of cations and anions.

### Step-by-Step Solution:

1. **Identify the Halides**: The halides of aluminum we need to consider are:
- AlI3 (Aluminum Iodide)
- AlBr3 (Aluminum Bromide)
- AlCl3 (Aluminum Chloride)
- AlF3 (Aluminum Fluoride)

2. **Recognize the Cation**: In all the halides mentioned, the cation (Aluminum ion, Al³⁺) is the same. Therefore, the difference in covalent character will depend on the anions.

3. **Analyze the Size of Anions**: According to Fajans' rules, the size of the anion plays a crucial role in determining the nature of the bond:
- Iodine (I⁻) > Bromine (Br⁻) > Chlorine (Cl⁻) > Fluorine (F⁻)
- This means that I⁻ is the largest anion and F⁻ is the smallest.

4. **Apply Fajans' Rules**: Fajans' rules state that:
- As the size of the anion increases (with the cation remaining constant), the covalent character of the compound increases while the ionic character decreases.
- Therefore, since I⁻ is the largest anion, it will have the highest covalent character when bonded with Al³⁺.

5. **Conclusion**: Based on the above analysis, AlI3 (Aluminum Iodide) has the most covalent character among the aluminum halides because it has the largest anion (I⁻). Thus, the correct answer is:
- **AlI3** (Aluminum Iodide).

### Final Answer:
The most covalent halide of aluminum is **AlI3**.