Final answer:
Bromine will gain one electron to form an ion, which aligns it with the electron configuration of the next noble gas, krypton.
Step-by-step explanation:
When bromine forms an ion, it will gain one electron. This is because bromine is a member of group 17 in the periodic table, also known as the halogens. Atoms from group 17 generally gain one electron to achieve the electron configuration of the next noble gas, forming an anion with a 1- charge. Bromine, in its neutral form, has 35 protons and 35 electrons. By gaining one electron, bromine becomes Br-, with 35 protons and 36 electrons, achieving a noble gas electron configuration similar to krypton.