Sacrificial anode protects iron of ships, underground pipelines etc. from rusting, a process known as cathodic protection. Which one of the following metals cannot be used as a sacrificial anode ?

Sacrificial anodes operate on the principle of cathodic protection, where a more reactive (less noble) metal is electrically connected to a structure to be protected, such as iron or steel [t3][t6]. For a metal to act as a sacrificial anode, it must have a more active electrochemical potential than the metal it is protecting, allowing it to oxidize preferentially [t2][t6]. According to the galvanic series, zinc, magnesium, and aluminium are more active than iron and are the standard metals used for this purpose [t3][t4]. Tin, however, is less reactive than iron (more noble) in the galvanic series. If tin were used, the iron would become the anode and corrode faster to protect the tin, which is the opposite of the desired effect. Therefore, tin cannot be used as a sacrificial anode for iron structures [t3][t8].

Sources

1. [1] https://www.sciencedirect.com/topics/chemistry/sacrificial-anode
2. [2] https://www.sciencedirect.com/topics/materials-science/galvanic-corrosion