Question

Which of the following metal cannot be used for cathodic protection of $Fe$?

• A. Zinc
• B. Aluminium
• C. Magnesium
• D. Copper

Answer 1

The correct option is D Copper

According to electrochemical series:
Standard Reduction Potential (SRP) follows the order:
$\underset{0.34V}{E_{C{u}^{2+}/Cu}^0}>\underset{-0.44V}{E_{F{e}^{2+}/Fe}^0}>\underset{-0.76V}{E_{Z{n}^{2+}/Zn}^0}>\underset{-1.66V}{E_{A{l}^{3+}/Al}^0}>\underset{-2.36V}{E_{M{g}^{2+}/Mg}^0}$
In cathodic protection, metal to be used for protection of iron should have a higher standard oxidation potential, and thus the metal should get oxidised.
From the above order, since copper has a higher standard reduction potential than iron, it cannot get oxidised and hence cannot be used for cathodic protection of $Fe$.