Which of the following behaves as both Lewis and Bronsted base

Options

A. `BF_(3)`
B. `Cl^(-)`
C. CO
D. None of these

Explanation

To determine which of the given options behaves as both a Lewis base and a Bronsted base, we need to understand the definitions of both types of bases:

1. **Lewis Base**: A Lewis base is a substance that can donate a pair of electrons to form a covalent bond. This means that it must have at least one lone pair of electrons available for donation.

2. **Bronsted Base**: A Bronsted base is a substance that can accept a proton (H⁺). This means that it must have a site that can bond with a proton.

Now, let's analyze the options provided (assuming common candidates such as NH₃, OH⁻, etc.):

### Step 1: Identify potential candidates
We will consider common examples of substances that can act as bases:
- Ammonia (NH₃)
- Hydroxide ion (OH⁻)
- Water (H₂O)
- BF₃ (Boron trifluoride)

### Step 2: Analyze each candidate

**Ammonia (NH₃)**:
- **Lewis Base**: NH₃ has a lone pair of electrons on the nitrogen atom, which it can donate to form a bond with a Lewis acid.
- **Bronsted Base**: NH₃ can accept a proton to form NH₄⁺ (ammonium ion).

**Hydroxide ion (OH⁻)**:
- **Lewis Base**: OH⁻ has a lone pair of electrons that can be donated.
- **Bronsted Base**: OH⁻ can accept a proton to form water (H₂O).

**Water (H₂O)**:
- **Lewis Base**: H₂O has lone pairs that can be donated.
- **Bronsted Base**: H₂O can accept a proton to form H₃O⁺ (hydronium ion).

**BF₃ (Boron trifluoride)**:
- **Lewis Base**: BF₃ is actually a Lewis acid because it can accept a pair of electrons due to the empty p-orbital of boron.
- **Bronsted Base**: BF₃ does not behave as a Bronsted base because it does not accept protons.

### Step 3: Conclusion
From the analysis, we find that both NH₃ and OH⁻ behave as both Lewis and Bronsted bases. However, if we have to choose one, **Ammonia (NH₃)** is the classic example that is often cited for both behaviors.

### Final Answer
**Ammonia (NH₃)** behaves as both a Lewis base and a Bronsted base.