Final answer:
Galvanized iron pipe has been dipped in molten zinc primarily to make it resistant to corrosion through a process known as galvanization. Zinc, being more reactive than iron, offers cathodic protection and ensures longevity of the pipe in corrosive environments.
Step-by-step explanation:
Galvanized iron pipe is coated with a thin layer of zinc through a process commonly known as galvanization. The primary purpose of this is to make the pipe resistant to corrosion. Galvanization works because zinc is a more reactive metal compared to iron. This means that zinc will react with oxygen more readily and will 'sacrifice' itself to protect the underlying iron.
Consequently even if the zinc layer is damaged, the iron beneath is safeguarded by cathodic protection, where the zinc layer is still able to protect the iron from corrosion. This makes galvanized iron pipes ideal for plumbing and outdoor applications where they may be exposed to moisture or corrosive elements. While it is true that galvanized iron pipes are also lightweight and can be a good conductor of electricity these are not the primary reasons for galvanizing iron. Thus the correct answer to the question is A. Resistant to corrosion.