Answer:
2Cu + O₂ => 2CuO
Step-by-step explanation:
I am assuming Copper II, the most common form as listed in order of commonality on the periodic table.
Write a skeleton equation
Cu + O₂ => CuO
Because oxygen is a diatomic atom, it must have 2 atoms when it is alone.
Balanced
2Cu + O₂ => 2CuO
The only way to increase the number of oxygen atoms in the right side is by doubling all of CuO.
As a result, I need 2 copper atoms on the left side also.
By doubling that, the equation is balanced.
Both sides have 2 copper and 2 oxygen atoms.