Final answer:
Metals corrode by undergoing redox reactions with their environment, with iron forming a reddish-brown hydrated metal oxide known as rust, which is not protective and continually flakes off.
Step-by-step explanation:
When metals corrode, they typically undergo a process known as oxidation, where they react with elements in their environment such as oxygen, forming new compounds. One of the most common examples of corrosion is the formation of rust on iron. This type of corrosion is a galvanic process that involves redox reactions. In the presence of oxygen and water, iron transforms into Fe2O3·xH2O, a reddish-brown hydrated metal oxide commonly referred to as rust. Unlike protective oxides such as those formed by aluminum or chromium, rust does not adhere well to the iron's surface and continually flakes off, exposing more metal to corrosion. This phenomenon significantly impacts industries, leading to substantial economic costs in maintaining and replacing corroded iron objects.