The compound that is not a Lewis acid is

Options

A. `BF_(3)`
B. `AICI_(3)`
C. `BeCI_(2)`
D. `NH_(3)`

Answer

To determine which compound is not a Lewis acid, we need to understand the definition of a Lewis acid. A Lewis acid is defined as a species that can accept an electron pair. This means that Lewis acids are typically electron-deficient species or electrophiles, often characterized by having an incomplete octet of electrons.

### Step-by-Step Solution:

1. **Identify the Definition of Lewis Acids**:
- Lewis acids are electron pair acceptors.
- They are often electron deficient and can have an incomplete octet.

2. **Analyze the Given Options**:
- We will evaluate each compound to see if it can accept an electron pair.

3. **Option 1: BF3 (Boron Trifluoride)**:
- Boron has 3 valence electrons and forms three bonds with fluorine, resulting in an incomplete octet.
- BF3 can accept an electron pair, making it a Lewis acid.

4. **Option 2: AlCl3 (Aluminum Chloride)**:
- Aluminum has 3 valence electrons and forms three bonds with chlorine, also resulting in an incomplete octet.
- AlCl3 can accept an electron pair, making it a Lewis acid.

5. **Option 3: BeCl2 (Beryllium Chloride)**:
- Beryllium has 2 valence electrons and forms two bonds with chlorine, leading to an incomplete octet.
- BeCl2 can accept an electron pair, making it a Lewis acid.

6. **Option 4: NH3 (Ammonia)**:
- Nitrogen has 5 valence electrons and forms three bonds with hydrogen, leaving one lone pair.
- NH3 has a complete octet and can donate its lone pair but cannot accept an electron pair. Therefore, it is not a Lewis acid.

7. **Conclusion**:
- The compound that is not a Lewis acid is **NH3 (Ammonia)**.

### Final Answer:
**NH3 (Ammonia)** is the compound that is not a Lewis acid.

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