Here's how to determine the number of valence electrons in NF3 (nitrogen trifluoride):

1. Valence Electrons of Each Atom:

* Nitrogen (N): Group 15 (or VA) on the periodic table, so it has 5 valence electrons.

* Fluorine (F): Group 17 (or VIIA), so it has 7 valence electrons.

2. Total Valence Electrons:

* Nitrogen: 1 atom * 5 valence electrons/atom = 5 valence electrons

* Fluorine: 3 atoms * 7 valence electrons/atom = 21 valence electrons

* Total: 5 + 21 = 26 valence electrons

Therefore, NF3 has 26 valence electrons.