Final answer:
The valence of selenium, typically -2, refers to its combining power based on its six valence electrons with the configuration 4s²4p⁴. In compounds, selenium tends to gain two electrons to fill its valence shell.
Step-by-step explanation:
The valence of selenium is the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.
Selenium has six valence electrons, as indicated by its valence electron configuration: 4s²4p⁴. This means in the fourth energy level (n = 4 shell), selenium has a total of six electrons that can interact with other atoms to form chemical bonds. The valence of selenium can vary depending on the type of compound it forms; however, it is typically -2, as it often seeks to gain two electrons to fill its valence shell and achieve a stable noble gas configuration.