Chromium(II) sulfate
this is an ionic compound of a metal and a polyatomic ion.
chromium is a metal that can form more than one type of cation. In this case, the polyatomic ion name is sulfate and it has 2 negative charges. Then Cr has to have 2 positive charges.
then write the name of the metal followed by the charge of the ion between parenthesis and in roman numbers followed by the name of the polyatomic ion.