The tendency of `bF_(3), BCl_(3)` and `BBr_(3)` behave as Lewis acid decreases in the sequnece

Options

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

Explanation

To determine the sequence in which the tendency of BF3, BCl3, and BBr3 to behave as Lewis acids decreases, we need to analyze the factors affecting their Lewis acidity.

### Step-by-Step Solution:

1. **Understanding Lewis Acids**:
- Lewis acids are defined as electron pair acceptors. They are typically electron-deficient species that can accept an electron pair from a Lewis base.

2. **Boron Compounds**:
- Boron, being an electron-deficient element, forms compounds like BF3, BCl3, and BBr3. In these compounds, boron has an incomplete octet, making them potential Lewis acids.

3. **Electron Deficiency and Overlap**:
- The ability of these boron compounds to act as Lewis acids depends on the extent of overlap between the boron’s empty p orbital and the filled p orbitals of the halogen atoms (F, Cl, Br).
- As we move from fluorine to iodine, the size of the halogen atoms increases, which affects the overlap.

4. **Analyzing the Halogens**:
- **Fluorine (F)**: Has a small atomic radius, allowing for good overlap with boron's empty p orbital. Therefore, BF3 is a strong Lewis acid.
- **Chlorine (Cl)**: Larger than fluorine, leading to slightly less effective overlap compared to BF3. Thus, BCl3 is a weaker Lewis acid than BF3.
- **Bromine (Br)**: Even larger than chlorine, resulting in even poorer overlap with boron. BBr3 is a weaker Lewis acid than BCl3.

5. **Conclusion**:
- The order of Lewis acidity based on the overlap and electron deficiency is: BBr3 < BCl3 < BF3.
- Therefore, the tendency of BF3, BCl3, and BBr3 to behave as Lewis acids decreases in the sequence: **BBr3 > BCl3 > BF3**.

### Final Answer:
The correct order of decreasing tendency to behave as Lewis acids is: **BBr3 > BCl3 > BF3**.