This is going to seem like a very elementary question. Let's look at a phosphate ion for example. 1) How can I tell by looking at the name that it's an oxyanion? I know it's a polyatomic ion with phosporous. 2) Since it actually IS an oxyanion of phosphorous and oxygen, how do I know how many of each element are in the molecular formula? My chemistry professor just told me to not worry about it because he's providing a chart of the cations and anions for the exam, but I'm trying to figure out what the concept is here that I'm missing. I want to take the DAT or MCAT next year, and I know we won't have any such charts to take the test with. Can someone help me out?