Here's why:
* Nitrogen (N) has a valency of 3, meaning it can form three bonds.
* Fluorine (F) has a valency of 1, meaning it can form one bond.
To satisfy the valencies of both elements, the correct formula must have one nitrogen atom bonded to three fluorine atoms: NF3.
The other options are incorrect:
* NF: This would only satisfy the valency of fluorine, not nitrogen.
* NF2: This would only satisfy the valency of fluorine, not nitrogen.
* N3F: This would only satisfy the valency of nitrogen, not fluorine.
