Final answer:
The oxidation number for copper in Cu2S is +2.
Step-by-step explanation:
The oxidation number or charge for copper in Cu2S is +2.
According to the rules of assigning oxidation states, elemental form copper has an oxidation state of 0, oxygen has an oxidation state of -2, and the sum of the oxidation states in a compound must equal the net charge. In Cu2S, the net charge is 0, which means each Cu atom must have a charge of +2. Since there are two Cu atoms, the overall oxidation number for copper is +2.