The correct option is Galvanisation.
Explanation
Corrosion involves the degradation of metals due to reactions with the environment. To prevent the rusting of iron, various coating techniques are utilized based on the chemical properties of the metals involved.
- Galvanisation is Correct: Galvanisation is the process of applying a protective zinc coating to iron or steel. Since zinc is more reactive than iron (placed higher in the reactivity series), it acts as a sacrificial anode. It corrodes in preference to iron, protecting the base metal even if the coating is scratched.
- Anodising is Incorrect: Anodising is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. It is most commonly associated with aluminium, not the zinc coating of iron.
- Tinning is Incorrect: Tinning refers to the process of coating a metal, such as iron or copper, with a thin layer of tin. While it provides a non-toxic barrier often used in food cans, tin is less reactive than iron and does not provide sacrificial protection.
- Electrorefining is Incorrect: Electrorefining is a process used to purify impure metals (such as copper) through electrolysis. It is a method of extraction and purification, not a protective coating technique.
Key Takeaway: Galvanisation is the specific metallurgical process of coating iron with zinc to prevent rusting through sacrificial protection.