Bromate ion has a charge of -1. This is because it consists of one bromine atom and three oxygen atoms. Bromine has an atomic number of 35, which means that it has 35 protons in its nucleus. Oxygen has an atomic number of 8, which means that it has 8 protons in its nucleus. Therefore, the bromate ion has a total of 35 + 3 x 8 = 67 protons. However, it also has 35 + 3 x 8 = 67 electrons, so it has a net charge of -1.