Answer:
Valence electrons
Explanation:
The formation of phosphorus trifluoride is orchestrated by the sharing of the valence electrons between phosphorus and fluorine.
This is called covalent bonding. In covalent bonding, elements with zero or very small electronegativity combines together. Such bonding occurs between non-metals.
For this bond to form, phosphorous shares its 5 electrons with the 3 of the fluorine.