Here's why:

* Electron Configuration: Oxygen's electron configuration is 1s² 2s² 2p⁴.

* Valence Electrons: Valence electrons are the electrons in the outermost energy level of an atom. For oxygen, this is the 2nd energy level (2s² 2p⁴).

* Total: There are 2 electrons in the 2s subshell and 4 electrons in the 2p subshell, giving a total of 6 valence electrons.