Magnesium is considered the most active material in the galvanic series. The galvanic series is a list that ranks metals and alloys by their electrochemical potential in a specific environment, usually in seawater. More active metals, such as magnesium, have a higher tendency to corrode compared to less active metals.
When magnesium is exposed to an electrolyte, it will oxidize readily and serve as an anode in galvanic couples. This quality makes magnesium an effective sacrificial anode in cathodic protection systems, where it is intentionally used to protect more noble metals from corrosion.
In contrast, metals like platinum and gold are much less active, meaning they are more cathodic and resistant to corrosion. This lower reactivity is why they are often used in applications where corrosion resistance is paramount, but it also means they will not provide the same protective benefits as more active metals when acting as sacrificial anodes.