The compound that combines Be (beryllium) and O (oxygen) is beryllium oxide (BeO).

Here's why:

* Beryllium is in group 2 of the periodic table, meaning it has a +2 charge as a cation (Be²⁺).

* Oxygen is in group 16, meaning it has a -2 charge as an anion (O²⁻).

* To form a neutral compound, the charges need to balance. Therefore, one beryllium ion (Be²⁺) combines with one oxygen ion (O²⁻) to form BeO.