Which metal is commonly used for galvanization, that is, coating iron or steel to prevent rusting?

Introduction / Context:
Galvanization is a widely used method of protecting iron and steel from rusting. In this process, a more reactive metal is coated on the surface of iron to provide sacrificial protection. Knowing which metal is used for galvanization is important in both basic chemistry and practical engineering applications. This question asks you to identify that protective metal.

Given Data / Assumptions:

• The process mentioned is galvanization, used to protect iron or steel.
• Options include zinc, copper, iron, silver, and aluminium.
• We assume standard industrial practice where galvanised iron sheets and pipes are common.
• The protective metal should be more reactive than iron and capable of forming a durable coating.

Concept / Approach:
In galvanization, iron or steel objects are dipped into molten zinc or coated with zinc by other methods such as electroplating. Zinc forms a protective physical barrier and also acts as a sacrificial anode. Because zinc is more reactive than iron, it corrodes preferentially, protecting the underlying iron from rusting. This technique is called hot dip galvanizing when the iron is dipped in molten zinc. Other metals such as copper, silver, or aluminium are used for different purposes but not for classical galvanization of iron.

Step-by-Step Solution:
Step 1: Remember that rusting is the corrosion of iron, forming hydrated iron oxides when exposed to oxygen and moisture. Step 2: To prevent rusting, a more reactive metal can be coated on the iron surface to shield it from the environment and provide sacrificial protection. Step 3: Zinc is commonly used for this purpose. Steel sheets are coated with zinc to produce galvanised iron used for roofing, fencing, and water pipes. Step 4: If the zinc coating is scratched, zinc still protects the exposed iron because it preferentially oxidises due to being more reactive. Step 5: Copper and silver are less reactive than iron and would not provide sacrificial protection in the same way. Step 6: Therefore, the metal used for galvanization is zinc.

Verification / Alternative check:
Industrial descriptions of galvanised steel always emphasise zinc coating. Product names such as galvanised iron sheets are directly linked with zinc coated steel. Textbook explanations of corrosion protection also use diagrams showing a zinc layer over iron or zinc blocks attached to ship hulls as sacrificial anodes. These examples consistently associate galvanization with zinc, not with other metals listed in the options.

Why Other Options Are Wrong:
Copper: Used in electrical wiring and decorative plating but is less reactive than iron and not standard for galvanization.
Iron: This is the metal being protected, not the coating metal; using iron itself as a coating would not prevent rust.
Silver: Valuable and less reactive than iron, used for jewellery and decorative plating but not for mass corrosion protection of steel structures.
Aluminium: Forms a protective oxide layer and is used in anodising, but galvanization specifically refers to zinc coating on iron or steel.

Common Pitfalls:
Students sometimes confuse galvanization with other surface treatments such as electroplating or anodising and may choose metals like copper or silver based on their familiarity with plating. Another mistake is simply guessing based on which metals sound more shiny or valuable. To answer correctly, remember that galvanization has a specific meaning in corrosion science: coating iron with zinc to protect it from rusting.

Final Answer:
Zinc is the metal used for galvanization of iron and steel.