Here's why:

* Sulfur's electron configuration: Sulfur has an atomic number of 16, meaning it has 16 protons and 16 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁴.

* Valence electrons: The outer valence shell is the highest energy level occupied by electrons. For sulfur, this is the third energy level (n=3).

* Counting valence electrons: The 3s and 3p orbitals are filled with a total of 6 electrons (2 in the 3s and 4 in the 3p).