Which galvanic anode would NOT be effective in providing cathodic protection to steel?

The choice of chromium as an anode for cathodic protection to steel is not effective due to its electrochemical potential when compared to the other metals listed. In cathodic protection systems, the anode must have a more negative electrochemical potential than the metal it aims to protect—in this case, steel.

Magnesium, aluminum, and zinc all possess relatively negative potentials in comparison to steel, making them suitable as sacrificial anodes. They corrode preferentially, thus providing protection to the steel structure they are paired with. This sacrificial behavior is essential to the functioning of a cathodic protection system, as the anode must corrode instead of the steel.

Chromium, on the other hand, is often used in stainless steel and does not exhibit a sufficiently negative electrochemical potential to serve effectively as a sacrificial anode. Instead, it can form a passive oxide layer that protects its own surface but does not provide the necessary cathodic protection required for the steel underneath. As a result, chromium is not suitable for use as a galvanic anode in cathodic protection systems for steel.