Here's why:

* Electronic Configuration: Beryllium's electron configuration is 1s² 2s².

* Valence Shell: The outermost shell (the 2nd shell in this case) is called the valence shell.

* Valence Electrons: The electrons in the valence shell are the valence electrons. In beryllium, the 2s² shell contains 2 electrons.

Therefore, beryllium has 2 valence electrons.