Which of following trihalides of nitrogen behaves as the weakest base?

Options

A. `NF_(3)`
B. `NCl_(3)`
C. `NBr_(3)`
D. `Nl_(3)`

Answer

To determine which of the nitrogen trihalides behaves as the weakest base, we need to analyze the basicity of each compound: NF3, NCl3, NBr3, and NI3.

### Step-by-Step Solution:

1. **Understanding Basicity**: Basicity refers to the ability of a compound to donate a lone pair of electrons. In the case of nitrogen trihalides, the nitrogen atom has one lone pair that can be donated.

2. **Electronegativity of Halogens**: The electronegativity of halogens decreases as we move down the group in the periodic table. This means that fluorine (F) is the most electronegative, followed by chlorine (Cl), bromine (Br), and iodine (I).

3. **Effect of Electronegativity on Basicity**:
- In NF3, the highly electronegative fluorine atoms attract the lone pair of electrons on nitrogen more strongly than the other halogens do. This strong attraction makes it harder for nitrogen to donate its lone pair, resulting in lower basicity.
- Conversely, as we move to NCl3, NBr3, and NI3, the electronegativity of the halogens decreases, which means the attraction to the lone pair on nitrogen decreases, allowing for easier donation of the lone pair and thus increasing basicity.

4. **Ranking the Basicity**:
- **NI3**: Least electronegative halogen (I) → Highest basicity.
- **NBr3**: Next least electronegative (Br) → Moderate basicity.
- **NCl3**: More electronegative (Cl) → Lower basicity.
- **NF3**: Most electronegative (F) → Lowest basicity.

5. **Conclusion**: Based on the analysis, NF3 has the weakest basic character among the nitrogen trihalides due to the strong attraction of the lone pair by the highly electronegative fluorine atoms.

### Final Answer:
The trihalide of nitrogen that behaves as the weakest base is **NF3**.

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