Answer:
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