Answer:
The third one:
![CuSO_4](https://img.qammunity.org/2022/formulas/chemistry/college/p4tophj50zmk6d76itsrlbn3rhgdrdbgtl.png)
Step-by-step explanation:
Again you are going to want to look at a periodic table so you can determine the symbol of each atom.
The symbol for copper is Cu, the symbol for sulfur is S and the symbol for Oxygen.
There is 1 atom of copper in the compound
So we have Cu
There is 1 atom of sulfur in the compound
So we would have CuS
There are 4 atoms of oxygen in the compound
So we would have
![CuSO_4](https://img.qammunity.org/2022/formulas/chemistry/college/p4tophj50zmk6d76itsrlbn3rhgdrdbgtl.png)
Note that the little number at the bottom left after each symbol indicates how many atoms of that element are in that compound.