Here's why:

* Electron Configuration: Hydrogen has only one proton and one electron. Its electron configuration is 1s¹. This means its only electron occupies the first energy level (n=1) and the s orbital.

* Valence Shell: The valence shell is the outermost shell of an atom that contains electrons. For hydrogen, the 1s orbital is its only shell, making it the valence shell.

* Valence Electrons: Valence electrons are the electrons found in the valence shell. Therefore, hydrogen has only one valence electron.