Final answer:
The electron configuration of Br- is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6, representing a noble gas configuration identical to that of krypton (Kr).
Step-by-step explanation:
The electron configuration of a bromide ion (Br-) is determined by adding an extra electron to the neutral bromine atom configuration. Neutral bromine has an atomic number of 35, which corresponds to the electron configuration of 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5. When an electron is added to form the Br- ion, the configuration becomes 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6.
Since bromine is in the halogen group, it readily gains one electron to achieve a noble gas configuration, which in this case is the same as krypton (Kr). Thus, the bromide ion Br- has a complete octet in its outermost shell, making it more stable than the neutral atom.