To create the strongest electromagnet, you would want to use materials that enhance the magnetic field produced by the electric current. The best combination would include:
- An iron nail (which serves as the core to enhance the magnetic field)
- Copper wire (which will carry the electrical current)
- The 6-volt battery (which provides a higher voltage, leading to a stronger current)
Therefore, the correct choice is:
iron nail, copper wire, 6-volt battery.