Final answer:
An atom of Be-9, like all isotopes of beryllium (Be), has four protons in its nucleus, consonant with its atomic number of 4.
Step-by-step explanation:
The number of protons in an atom is indicated by its atomic number. For the alkaline earth metal beryllium (Be), which has an atomic number of 4, there are four protons in its nucleus. No matter the isotope, the number of protons remains the same; thus, for Be-9, the number of protons is also four.
Beryllium's electrons are distributed in the 1s and 2s subshells, with its electron configuration being 1s²2s². However, the neutron count can change among isotopes without altering the number of protons or electrons, which define the element's chemical properties.