In corrosion protection of iron, the industrial process of depositing a protective layer of zinc on the surface of iron objects is called ___________.

Introduction / Context:
Preventing rust and corrosion of iron and steel is crucial in construction, transportation and many household applications. One widely used method is to coat iron with a layer of zinc, which protects the underlying metal from contact with moisture and oxygen. This process is known by a specific name in basic metallurgy and materials science, and many general science exams test whether learners can correctly identify it.

Given Data / Assumptions:
- The process involves depositing a layer of zinc metal on iron or steel surfaces.
- The goal is corrosion protection by forming a barrier and providing sacrificial protection.
- Options include common physical and chemical processes such as crystallisation and baking.
- We assume standard industrial terminology used in school and competitive examinations.

Concept / Approach:
Coating iron with zinc to prevent corrosion is called galvanisation. In hot dip galvanising, iron or steel objects are cleaned and then dipped into molten zinc, which adheres to the surface. The zinc layer protects the iron both by acting as a physical barrier and by functioning as a sacrificial anode, since zinc is more reactive than iron and will corrode preferentially. Crystallisation, baking, tempering and rusting refer to entirely different processes and do not describe the protective zinc coating method.

Step-by-Step Solution:
Step 1: Identify the key action in the question, which is depositing a layer of zinc onto iron. Step 2: Recall the name given to the standard process where steel or iron is dipped into molten zinc to form a protective coating. Step 3: Recognise that this process is called galvanisation or galvanizing, widely used for pipes, roofing sheets and structural components. Step 4: Compare other terms: crystallisation refers to formation of crystals from a solution, baking is a heating process in food or ceramics, and tempering is heat treatment of steel, none of which involve applying zinc. Step 5: Conclude that galvanisation is the only term that matches the description of coating iron with zinc to prevent corrosion.

Verification / Alternative check:
You can check common examples from daily life. Many fences, buckets and roofing sheets are labelled as galvanised iron, indicating that they have been coated with zinc. Textbooks on metals and non metals usually provide diagrams of hot dip galvanising and explicitly state that the process is used to prevent rusting of iron. Rusting itself is the corrosion of iron and is the phenomenon that galvanisation tries to prevent, not the name of the protective process. This repeated exposure in textbooks confirms galvanisation as the correct answer.

Why Other Options Are Wrong:
Crystallisation deals with purification of solids by forming crystals from solutions and has nothing to do with zinc coatings. Rusting is the slow oxidation of iron that produces hydrated iron oxides and is the problem galvanisation is meant to solve. Baking is a general heating process used mainly in food preparation and some industrial curing steps, not specifically associated with zinc coatings. Tempering is a heat treatment method used to adjust hardness and toughness of steel and does not involve applying zinc. None of these describe the zinc coating method on iron surfaces.

Common Pitfalls:
A common confusion is between electroplating and galvanisation, since both involve coating metals. Electroplating uses electric current to deposit a metal layer from a solution, whereas hot dip galvanisation uses molten zinc. Another pitfall is mixing up rusting, which is corrosion, with methods used to prevent it. Remembering that galvanised iron refers to zinc coated iron makes it easier to associate the word galvanisation with protective zinc coating processes.

Final Answer:
The process of depositing a protective layer of zinc on iron is called Galvanisation.