Selenium, when it forms an ion, typically gains two electrons to achieve a stable electron configuration. This means that the ionic charge of selenium is -2.
Here’s why: Selenium is a member of group 16 in the periodic table, which is also known as the chalcogen group. Elements in this group have six valence electrons. To become stable, selenium can gain two additional electrons to fill its outer shell, reaching a total of eight valence electrons. This gain of electrons gives selenium a negative charge of -2, resulting in the formation of the selenide ion (Se2-).