Here's why:

* Electron Configuration: Beryllium (Be) has an atomic number of 4, meaning it has 4 protons and 4 electrons. Its electron configuration is 1s² 2s².

* Valence Electrons: Valence electrons are the electrons in the outermost shell of an atom. In beryllium's case, the outermost shell is the second shell (2s²), which contains 2 electrons.