Here's why:
* Electron Configuration: Selenium's electron configuration is [Ar] 3d10 4s2 4p4.
* Valence Shell: The outermost shell (the 4th shell) contains the valence electrons.
* Valence Electrons: There are 2 electrons in the 4s subshell and 4 electrons in the 4p subshell, for a total of 6 valence electrons.
