Question

iron bridges are coated with zinc why

Answer 1

To prevent rusting of bridges, due to oxidation of iron.Zinc forms a layer on the iron that prevents contact between iron and air.

Answer 2

Iron bridges are coated with zinc. This process is called Galvanization and it is done to prevent rusting (corrosion) of iron. Zinc forms a layer between iron and the atmosphere (with oxygen and water vapour). Zinc is a more electro positive metal, thus it gets oxidized first to zinc oxide, thus saving the iron from getting rusted!!