Answer
Six valance electrons; Gain electrons.
Work Step by Step
Selenium is a main group element. Therefore, its valance electrons are those in the outermost energy principal level. The noble gas configuration for selenium is $[Ar]4s^{2}3d^{10}4p^{4}$. Therefore, selenium has six valance electron. Since, Selenium is a non-metal, it will gain electrons in chemical reactions.
