The correct answer is A. Zinc.
Galvanized iron is made by coating iron with a thin layer of zinc. This process is called galvanization and it helps to protect the iron from rust and corrosion. Zinc is a very reactive metal and it forms a protective layer on the surface of the iron that prevents oxygen and water from reaching the iron itself. This layer is very thin, but it is very effective at preventing rust.
Galvanized iron is often used in construction and manufacturing because it is a very durable material. It is also used in products such as nails, screws, and bolts. Galvanized iron is a safe and environmentally friendly material and it is a good choice for many applications.
The other options are incorrect because they are not metals that are used to galvanize iron. Nickel, chromium, and sulfur are all metals that are used in other types of metal coatings, but they are not used to galvanize iron.