The strongest Lewis acid among the following is :

Options

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

Answer

To determine the strongest Lewis acid among the given options (BF3, BBr3, BI3, BCl3), we need to analyze the electron-accepting ability of each compound. A Lewis acid is defined as a species that can accept an electron pair, which typically requires the presence of vacant orbitals.

### Step-by-Step Solution:

1. **Understand the Concept of Lewis Acids**:
- Lewis acids are electron pair acceptors. They must have vacant orbitals to accept electrons.

2. **Identify the Compounds**:
- The compounds given are:
- BF3 (Boron Trifluoride)
- BBr3 (Boron Tribromide)
- BI3 (Boron Triiodide)
- BCl3 (Boron Trichloride)

3. **Analyze the Electron Configuration of Boron**:
- Boron (B) has the electron configuration of 1s² 2s² 2p¹, which means it can form three bonds but has only six electrons in its valence shell. Therefore, it can accept electrons to complete its octet.

4. **Evaluate Each Compound**:
- **BF3**:
- Boron is bonded to three fluorine atoms. Fluorine is highly electronegative and can engage in back-donation of electrons, which can stabilize the molecule. However, this back-donation reduces the Lewis acidity of BF3.
- **BCl3**:
- Chlorine is less electronegative than fluorine, leading to less effective back-donation compared to BF3. Thus, BCl3 is a stronger Lewis acid than BF3.
- **BBr3**:
- Bromine is even less electronegative than chlorine, resulting in even less back-donation. Therefore, BBr3 is a stronger Lewis acid than BCl3.
- **BI3**:
- Iodine is the least electronegative of the halogens listed. The back-donation effect is minimal, making BI3 the strongest Lewis acid among the four.

5. **Conclusion**:
- Among BF3, BCl3, BBr3, and BI3, the strongest Lewis acid is **BI3** due to the minimal back-donation effect from iodine, allowing boron to maintain its vacant orbitals and accept electrons effectively.

### Final Answer:
The strongest Lewis acid among the following is **BI3 (Boron Triiodide)**.