If a neutral atom of Bromine (Br) was to gain another electron, it would have the same electron configuration as which element?

Krypton (Kr)

Explanation:

We'll begin by writing the electronic configuration of bromine. This is illustrated below:

Br (35) => [Ar]4s² 3d¹⁰ 4p⁵

Since the bromine atom gains an extra electron, the number of electrons in the bromide ion, Br¯ becomes 36. Hence the electronic configuration of the bromide ion, Br¯ can be written as follow:

Br¯ (36) => [Ar]4s² 3d¹⁰ 4p⁶

Now, comparing the number of electrons in the bromide ion, Br¯ with those in the periodic table, it is evident that the bromide ion, Br¯ has the same number of electrons with krypton, Kr. Hence, the bromide ion, Br¯ and the krypton, Kr has the same electronic configuration i.e

Br¯ (36) => [Ar]4s² 3d¹⁰ 4p⁶

Kr (36) => [Ar] 4s² 3d¹⁰ 4p⁶