The correct answer is option 2 - Iron. Corrosion is the process of gradual destruction of a material due to chemical reactions with its environment. It usually involves the formation of oxides or salts on the surface of the material. Out of the given options, iron is the element that corrodes rapidly.

Iron is a highly reactive metal and readily reacts with oxygen in the presence of moisture to form iron oxide, commonly known as rust. This corrosion process weakens the iron structure and can lead to the degradation of objects made from iron, such as tools, bridges, or iron-based alloys.

While aluminum is also prone to corrosion, it forms a protective oxide layer that slows down the process. Zinc, on the other hand, is often used as a sacrificial coating to protect other metals from corrosion. Silver, being a noble metal, is highly resistant to corrosion and does not easily react with other substances.

Therefore, out of the given options, iron is the element that corrodes rapidly.