The charge of a beryllium-9 nucleus is +4.
This is because the beryllium-9 nucleus contains 4 protons, and since protons carry a positive charge, the total charge of the nucleus is the sum of the charges of all the protons. In a neutral atom, the number of electrons would equal the number of protons, resulting in no overall charge. However, when we talk about the nucleus alone, we focus solely on the protons. Therefore, the charge of the beryllium-9 nucleus is +4.