Which mental has the most negative potential when measured relative to copper/copper sulfate reference electrode?

Magnesium has the most negative potential when measured relative to a copper/copper sulfate reference electrode. This characteristic is significant because it indicates that magnesium can act as a more effective anode in cathodic protection systems. The potential measurement reflects the metal's tendency to corrode; a more negative potential suggests a higher reactivity and a higher likelihood of dissolving in an electrolytic environment.

In the context of cathodic protection, magnesium is often used as a sacrificial anode because it corrodes preferentially to the steel or iron structures it protects. This helps prevent the more valuable infrastructure from corroding and extends its useful life. Other metals, like aluminum and iron, have less negative potentials compared to magnesium, making them less efficient for this cathodic protection purpose. Carbon, being a non-metal, does not corrode in the same manner as the metals in the options, further distinguishing magnesium as the option with the most negative potential.