The correct Lewis acid order for boron halides is

Options

A. `BBr_(3) gt BCl_(3) gt Bl_(3) gt BF_(3)`
B. `BI_(3) gt BF_(3) gt BBr_(3) gt BCl_(3)`
C. `BF_(3) gt BCl_(3) gt BBr_(3) gt Bl_(3)`
D. `BI_(3) gt BBr_(3) gt BCl_(3) gt BF_(3)`

Answer

To determine the correct Lewis acid order for boron halides (BX3 where X = F, Cl, Br, I), we need to analyze the factors that influence the Lewis acidity of these compounds.

### Step-by-Step Solution:

1. **Understanding Lewis Acids**:
- A Lewis acid is defined as a species that can accept a pair of electrons. In the case of boron halides, boron (B) has an incomplete octet and can accept electron pairs from Lewis bases.

2. **Electronegativity of Halides**:
- The electronegativity of the halides decreases in the order: F > Cl > Br > I.
- More electronegative halides create greater electron density around boron, leading to increased inter-electronic repulsion. This makes it harder for the boron to accept electron pairs.

3. **Size of Halides**:
- As we move down the group from fluorine to iodine, the size of the halides increases. Larger halides (like I) can stabilize the positive charge on boron better than smaller halides (like F), making it easier for boron to accept electron pairs.

4. **Degree of Hydrolysis**:
- The degree of hydrolysis for boron halides increases from fluorine to iodine. This means that boron halides with larger halides (like I) are more likely to undergo hydrolysis and thus exhibit stronger Lewis acid behavior.

5. **Conclusion on Lewis Acid Strength**:
- Considering the above points, we can conclude that the Lewis acidity of boron halides increases in the order:
\[ \text{B}I_3 > \text{B}Br_3 > \text{B}Cl_3 > \text{B}F_3 \]

6. **Final Answer**:
- Therefore, the correct Lewis acid order for boron halides is:
\[ \text{B}I_3 > \text{B}Br_3 > \text{B}Cl_3 > \text{B}F_3 \]