* Electron Configuration: Sulfur's electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁴.

* Core Electrons: Core electrons are the electrons in the inner shells (all shells except the outermost valence shell).

* Valence Electrons: The outermost shell (in this case, the 3rd shell) contains the valence electrons (3s² 3p⁴).

So, the core electrons are those in the first and second shells (1s² 2s² 2p⁶), totaling 10 electrons.