Which of the following is not a Lewis acid ?

Options

A. `BBr_(3)`
B. `BF_(3)`
C. `BCl_(3)`
D. `[BH_(4)]^(Ө)`

Explanation

To determine which of the given compounds is not a Lewis acid, we need to analyze each option based on the definition of a Lewis acid. A Lewis acid is a substance that can accept an electron pair.

1. **BBr3**:
- The structure of BBr3 consists of a boron atom bonded to three bromine atoms.
- Boron has only 6 electrons in its valence shell (3 bonds with bromine), making it electron-deficient.
- Since it can accept an electron pair to complete its octet, BBr3 acts as a Lewis acid.

2. **BF3**:
- In BF3, boron is bonded to three fluorine atoms.
- Similar to BBr3, boron in BF3 has only 6 electrons in its valence shell.
- It is also electron-deficient and can accept an electron pair, thus BF3 is a Lewis acid.

3. **BCl3**:
- BCl3 has a boron atom bonded to three chlorine atoms.
- Boron again has only 6 electrons in its valence shell.
- It can accept an electron pair to complete its octet, making BCl3 a Lewis acid as well.

4. **BH4-**:
- The BH4- ion (tetrahydroborate) has a boron atom bonded to four hydrogen atoms and carries a negative charge.
- In this case, boron has a total of 8 electrons (4 bonds with hydrogen), which means its octet is complete.
- Since it does not have the ability to accept an electron pair, BH4- does not act as a Lewis acid.

**Conclusion**: The compound that is not a Lewis acid is **BH4-**.