Here's why:

* Atomic Structure: Hydrogen has only one proton and one electron.

* Electron Configuration: Its electron configuration is 1s¹. This means its single electron occupies the first energy level (n=1) and the 's' subshell.

* Valence Shell: The outermost energy level of an atom is called its valence shell. Since hydrogen only has one energy level, that level is also its valence shell.

Therefore, the single electron in hydrogen is its valence electron.