Here's why:

* Electron Configuration: Potassium has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹.

* Valence Electrons: Valence electrons are the electrons in the outermost energy level of an atom. In the case of potassium, the outermost energy level is the 4th energy level, and it contains only one electron.

Let me know if you'd like to know about the valence electrons of other elements!