Arrange the following species in increasing order of bond angle
`NF_(3), NCl_(3) , NBr_(3) , NI_(3)`

Options

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

Answer

To arrange the species `NF₃`, `NCl₃`, `NBr₃`, and `NI₃` in increasing order of bond angle, we need to consider the factors that influence bond angles in these molecules. The bond angles are primarily affected by the electronegativity of the atoms bonded to nitrogen and the presence of lone pairs of electrons.

### Step-by-Step Solution:

1. **Identify the Structure of Each Molecule:**
- All four species have a central nitrogen atom (N) bonded to three halogen atoms (F, Cl, Br, I) and have one lone pair of electrons on nitrogen.
- The molecular geometry for all these compounds is trigonal pyramidal due to the lone pair.

2. **Electronegativity of Halogens:**
- The electronegativity of the halogens decreases in the order: F > Cl > Br > I.
- Fluorine (F) is the most electronegative, followed by chlorine (Cl), bromine (Br), and iodine (I).

3. **Effect of Electronegativity on Bond Angles:**
- The more electronegative the halogen, the more it attracts the shared electron pair towards itself. This reduces the repulsion between the bond pairs, leading to a larger bond angle.
- Conversely, as we move down the group from F to I, the bond pair-bond pair repulsion increases due to the larger size and lower electronegativity of the halogens, which results in smaller bond angles.

4. **Order of Bond Angles:**
- Since `NF₃` has fluorine (most electronegative), it will have the largest bond angle.
- `NCl₃` will have a smaller bond angle than `NF₃` because chlorine is less electronegative than fluorine.
- `NBr₃` will have a smaller bond angle than `NCl₃` due to bromine being less electronegative than chlorine.
- `NI₃` will have the smallest bond angle because iodine is the least electronegative and largest atom among the halogens.

5. **Final Arrangement:**
- Therefore, the increasing order of bond angles is:
- NI₃ < NBr₃ < NCl₃ < NF₃

### Conclusion:
The increasing order of bond angles for the species is:
**NI₃ < NBr₃ < NCl₃ < NF₃**