Selenium (Se) has an atomic number of 34, meaning it has 34 electrons. To achieve a noble gas configuration, it needs to gain two electrons.

Here's why:

* Selenium's electron configuration: [Ar] 3d¹⁰ 4s² 4p⁴

* Nearest noble gas (Krypton): [Ar] 3d¹⁰ 4s² 4p⁶

By gaining two electrons, Selenium fills its 4p subshell and achieves the same electron configuration as Krypton, which is a stable, noble gas configuration.