Which nitrogen trihalides is least basic

Options

A. `NF_3`
B. `NCl_3`
C. `NBr_3`
D. `NI_3`

Explanation

To determine which nitrogen trihalide is the least basic, we need to analyze the basicity of the nitrogen trihalides: NF3, NCl3, NBr3, and NI3. Basicity in this context is related to the availability of the lone pair of electrons on the nitrogen atom for donation.

### Step-by-Step Solution:

1. **Identify the Nitrogen Trihalides**: The nitrogen trihalides we are considering are NF3 (nitrogen trifluoride), NCl3 (nitrogen trichloride), NBr3 (nitrogen tribromide), and NI3 (nitrogen triiodide).

2. **Understand Basicity**: Basicity is the ability of a compound to donate a lone pair of electrons. In nitrogen trihalides, the nitrogen atom has a lone pair that can be donated.

3. **Electronegativity of Halogens**: The electronegativity of the halogens decreases in the order: F > Cl > Br > I. This means that fluorine is the most electronegative, followed by chlorine, bromine, and iodine.

4. **Effect of Electronegativity on Basicity**: The more electronegative the halogen, the more it will attract the electron density from the nitrogen atom. This reduces the availability of the lone pair on nitrogen for donation.

5. **Analyze Each Trihalide**:
- **NF3**: Fluorine is highly electronegative, which pulls the electron density away from nitrogen, making the lone pair less available for donation.
- **NCl3**: Chlorine is less electronegative than fluorine, so the lone pair on nitrogen is more available compared to NF3.
- **NBr3**: Bromine is even less electronegative than chlorine, further increasing the availability of the lone pair.
- **NI3**: Iodine is the least electronegative among these halogens, making the lone pair on nitrogen the most available for donation.

6. **Conclusion**: Since NF3 has the most electronegative halogen (fluorine), it will have the least availability of the lone pair for donation, making it the least basic of the nitrogen trihalides.

### Final Answer:
The nitrogen trihalide that is least basic is **NF3**.