Which of the following describes correct sequence for decreasing Lewis acid nature?

Options

A. `BCl_(3)gtBF_(3)gtBBr_(3)`
B. `BBr_(3)gtBCl_(3)gtBF_(3)`
C. `BBr_(3)gtBF_(3)gtBCl_(3)`
D. `BF_(3)gtBCl_(3)gtBBr_(3)`

Explanation

To determine the correct sequence for decreasing Lewis acid nature among the compounds \( BF_3 \), \( BCl_3 \), and \( BBr_3 \), we need to analyze the concept of Lewis acids and the role of backbonding.

### Step-by-Step Solution:

1. **Understand Lewis Acids**:
- Lewis acids are substances that can accept electron pairs. The ability of a Lewis acid to accept electrons is influenced by its electronic structure and the presence of backbonding.

2. **Identify the Compounds**:
- The compounds in question are \( BF_3 \), \( BCl_3 \), and \( BBr_3 \). Each of these compounds has a central boron atom (B) bonded to three halogen atoms (F, Cl, Br).

3. **Consider Backbonding**:
- Backbonding occurs when the lone pairs of electrons from the halogen atoms can be donated to the empty p-orbital of boron. The extent of backbonding affects the Lewis acidity:
- More backbonding means a stronger bond between boron and the halogen, which reduces the ability of boron to accept additional electron pairs (thus decreasing its Lewis acidity).

4. **Analyze the Halogens**:
- The halogens in the compounds are \( F \), \( Cl \), and \( Br \).
- Fluorine (F) has a small atomic size and can form strong backbonding with boron due to effective orbital overlap.
- Chlorine (Cl) has a larger atomic size than fluorine, resulting in less effective backbonding.
- Bromine (Br) has an even larger atomic size, leading to the least effective backbonding.

5. **Rank the Lewis Acids**:
- Since \( BF_3 \) has the strongest backbonding, it is the weakest Lewis acid.
- \( BCl_3 \) has moderate backbonding and is a stronger Lewis acid than \( BF_3 \).
- \( BBr_3 \) has the least backbonding and is the strongest Lewis acid among the three.

6. **Conclusion**:
- The decreasing order of Lewis acid nature is:
\[ BBr_3 > BCl_3 > BF_3 \]

### Final Answer:
The correct sequence for decreasing Lewis acid nature is \( BBr_3 > BCl_3 > BF_3 \).