# What is the simplest formula for chromium (II) and selenide?

$C r S e$
There is a chromium selenide, a simple binary salt. How do I know that selenium has a $- I I$ oxidation state? Consult the Periodic Table; there should be one beside you now. Selenium (like oxygen) is a chalcogen, and lies in the same Group as oxygen; it should, therefore, exhibit similar oxidation states.