In materials science and construction, galvanised iron sheets are steel or iron sheets that have been coated with which metal to protect them from rusting?

Introduction / Context:
Iron and steel are widely used in construction, roofing, and everyday products, but they can rust when exposed to moisture and air. To prevent rusting, a protective coating of another metal is often applied. When iron or steel sheets are coated in this way, they are called galvanised sheets. Knowing which metal is used in galvanisation is a common general science and engineering question.

Given Data / Assumptions:
- The material mentioned is galvanised iron sheets.
- The question asks which metal coats these sheets.
- Options include aluminium, copper, zinc, and tin.
- We assume the standard hot dip or electro galvanising process used in industry.

Concept / Approach:
Galvanisation is the process of coating iron or steel with a protective layer of zinc. Zinc acts as a physical barrier to moisture and oxygen and also provides sacrificial protection, meaning it corrodes preferentially to the underlying iron. This significantly delays rust formation on the base metal. Aluminium and tin are also used as coatings for some purposes, but those processes are not called galvanising; for example, tin plating produces tin cans. Copper is rarely used as a protective coating for steel against rust because it can encourage galvanic corrosion in some environments. Therefore, galvanised iron sheets specifically have a coating of zinc.

Step-by-Step Solution:
Step 1: Recall that galvanisation refers to coating iron or steel with zinc. Step 2: Understand that zinc protects iron by forming a barrier and by sacrificial corrosion. Step 3: Recognise that aluminium and tin coatings exist but are called by other names, not galvanisation. Step 4: Compare the options and identify zinc as the metal that matches the galvanising process. Step 5: Select zinc as the correct answer for the coating on galvanised iron sheets.

Verification / Alternative check:
Engineering and materials science books describe galvanised steel as steel coated with a layer of zinc, usually by dipping in molten zinc (hot dip galvanising). Commercial products such as roofing sheets, wire, and pipes often specify that they are zinc coated or galvanised for corrosion resistance. No reliable source describes galvanised sheets as coated with aluminium, copper, or tin as the standard process. This consistency confirms that zinc is the correct metal associated with galvanised iron sheets.

Why Other Options Are Wrong:
- Aluminium coatings are used in some specialised applications but are not generally referred to as galvanisation in basic science.
- Copper is not widely used as a rust preventing coating on steel and does not correspond to the galvanisation process.
- Tin plating is used for food containers and other items but produces tinned iron or tin cans, not galvanised iron sheets.

Common Pitfalls:
Learners may confuse different metal coating processes and assume that any protective metal layer counts as galvanising. Others may think of tin cans and mistakenly connect tin with galvanised sheets. A helpful memory trick is to remember the phrase zinc galvanising or zinc coated steel, which often appears on construction material descriptions. Linking galvanisation specifically with zinc helps avoid confusion and ensures the correct answer is chosen in exam questions.

Final Answer:
Galvanised iron sheets are coated with Zinc to protect them from rusting.