What are the oxidation states of copper?
This is too broad a question, you can't memorize its oxidation states, per se, but you can rationalize what it is by memorizing the rules for common anions it usually bonds with!
We know sulfate's charge is 2-, and we also memorize that an oxide anion has an oxidation state of 2-, unless its a peroxide in which case its charge is 1-, but that's another question!
So, solving this 8th grade algebra problem, we get:
Thus, in this particular compound, copper's oxidation state is 2+!
-2, +1, +2, +3, +4
Copper can have any of the above oxidation states, however +1 and +2 are the most common.
An example of a +2 oxidation state is CuO, where oxygen has an oxidation number of -2 and therefore copper has the oxidation number of +2 to balance out the molecule.
An example of a +1 oxidation state is Cu2O, where, once again, oxygen's oxidation state is -2 and so to balance out the molecule, each copper atom is +1.