A nucleophilic reagent is

Options

A. `CO_2`
B. `BF_3`
C. `dAlCl_3`
D. `NH_3`

Explanation

To determine which of the given options is a nucleophilic reagent, we need to understand what a nucleophile is. A nucleophile is a species that has a lone pair of electrons or a negative charge and is capable of donating these electrons to an electrophile (a species that accepts electrons).

Let's analyze the options one by one:

1. **Option A: Carbon Dioxide (CO₂)**
- The structure of carbon dioxide shows that carbon is bonded to two oxygen atoms with double bonds. Oxygen is more electronegative than carbon, leading to a partial negative charge on the oxygen atoms and a partial positive charge on the carbon atom. This makes carbon dioxide stable and more likely to act as an electrophile rather than a nucleophile.
- **Conclusion**: Carbon dioxide is not a nucleophilic reagent.

2. **Option B: Boron Trifluoride (BF₃)**
- Boron has an incomplete octet with three fluorine atoms bonded to it. Boron has an empty p orbital, which makes BF₃ electron-deficient. It tends to accept a pair of electrons, acting as an electrophile.
- **Conclusion**: Boron trifluoride is not a nucleophilic reagent.

3. **Option C: Aluminum Chloride (AlCl₃)**
- Similar to BF₃, aluminum chloride has an incomplete octet and a vacant p orbital. It can accept a pair of electrons, thus acting as an electrophile.
- **Conclusion**: Aluminum chloride is not a nucleophilic reagent.

4. **Option D: Ammonia (NH₃)**
- Ammonia has a nitrogen atom with a lone pair of electrons. This lone pair can be donated to an electrophile, making ammonia a nucleophile.
- **Conclusion**: Ammonia is a nucleophilic reagent.

**Final Answer**: The nucleophilic reagent among the options provided is **Ammonia (NH₃)**.