The DAT general chemistry section expects you to be fluent in chemical compounds. For example, do you know the formula for chromate? Below is a selected list of common ions you should know for the DAT (click for full image).
* Also, a common mistake I see is people thinking helium is a diatomic molecule (He2). The formula for helium gas is just He. Helium is a noble gas and already has a full shell, so it is very unreactive.