To achieve the same electron configuration as Krypton, Bromine (Br) with an atomic number of 35, needs to lose 7 electrons.

The electron configurations of Bromine and Krypton are:

Bromine (Br): 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵

Krypton (Kr): 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶

By losing 7 electrons, specifically the outermost 4s² and 3d¹⁰ electrons, Bromine will have the same electron configuration as Krypton. This results in the following configuration:

Bromine after losing 7 electrons: 1s²2s²2p⁶3s²3p⁶

Now, Bromine has the same electron configuration as Krypton, making it an isoelectronic species.