Which of the following neutral elements has the same electron configuration as the bromide ion, Br-?

A) iodine

B) krypton

C) chlorine

D) argon

B) krypton

Explanation:

Electron configuration of Br: [Ar] 3d10 4s2 4p5

Since we have the bromide ion with a negative charge, Br's atom acquired an electron and therefore another electron is added to the electronic configuration.

Electron configuration of Br-: [Ar] 3d10 4s2 4p6

And now this electronic configuration coincides with that of Krypton as we see below:

Electron configuration of Kr: [Ar] 3d10 4s2 4p6