Table
Graph
Conclusion
At 2 V, constantan and nichrome have a similar current between 0 and 0.1 A. Meanwhile, iron has a current of 0.3 A. As the voltage increased, the nichrome and constantan currents increased at a slow, steady rate. Meanwhile, iron had a sharp increase in current. Finally, at 10 V, nichrome is at 0.14 A, while constantan has almost double the amps. However, iron has a much higher current at around 1.6 A.
This tells me that iron has the lowest resistance because it has the highest current, and resistance lowers current. Nichrome has the lowest current and, therefore, has the highest resistance.