Here's how to determine the number of valence electrons in S²⁻:

* Start with the neutral atom: Sulfur (S) is in group 16 (VIA) of the periodic table, meaning it has 6 valence electrons.

* Consider the charge: The 2- charge indicates that the sulfur atom has gained two extra electrons.

* Add the electrons: 6 (original valence electrons) + 2 (gained electrons) = 8 valence electrons.

Therefore, S²⁻ has 8 valence electrons.