Final answer:
Copper has an oxidation state of +1 in CuBr, as demonstrated by the rules for assigning oxidation states and the need to balance the -1 charge of bromine.
Step-by-step explanation:
The oxidation state of copper is +1 in CuBr. By applying the rules of assigning oxidation states, we can discern that in the compound Cu(C2H3O2)2, copper has an oxidation state of +2 because the acetate ion (C2H3O2−) has a charge of -1 and there are two acetates for each copper.
For CuO, copper must have a +2 charge to balance the -2 charge of the oxide ion. CuC2O4 (copper oxalate) has an overall neutral charge, where oxalate (C2O42−) is -2, thus copper must be +2 to balance. Lastly, in CuBr, we have copper paired with bromine (Br), which has an oxidation state of -1, so for the overall neutral compound CuBr, copper must be in the +1 oxidation state, hence the answer is option D.