Bromine (Br) is a chemical element with atomic number 35. To determine the number of core electrons in an atom of bromine, we need to look at its electron configuration. The electron configuration of bromine is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵.
The core electrons of an atom are those that are located in the inner energy levels or shells, and they are not involved in chemical bonding. In the case of bromine, the inner energy levels are the 1s, 2s, and 2p orbitals. So, let's count the number of electrons in those orbitals:
1s² 2s² 2p⁶ = 10 electrons.
Therefore, bromine has 10 core electrons.