Here's why:

* Beryllium's electron configuration: Beryllium has an atomic number of 4, meaning it has 4 protons and 4 electrons. Its electron configuration is 1s²2s².

* Tendency to lose electrons: Beryllium has a relatively low ionization energy, meaning it takes less energy to remove an electron from its outermost shell. It tends to lose its two valence electrons (from the 2s orbital) to achieve a stable electron configuration like helium (1s²).

* Formation of a cation: When beryllium loses its two valence electrons, it forms a cation with a +2 charge, written as Be²⁺.

Therefore, Beryllium forms a positive ion because it loses electrons to achieve a stable electronic configuration.