Answer:
1. CuO, 2. O2, and 3. Cu2O.
Step-by-step explanation:
You can identify that we can state a synthesis reaction between Cu2O and O2 to form CuO:

The reactants are Cu2O and O2, and the product is CuO.
The answer would be 1. CuO, 2. O2, and 3. Cu2O.