Imagine carefully weighing a metal can, leaving it out in the rain for weeks and weeks
until it was very rusted, and then carefully weighing it again. Would the can be heavier or lighter after it was rusted? Why?
The answer would be heavier, though it depends upon the type of metal. Rusting is essentially corrosion. Rust is often caused by a piece of metal getting soaked in water and then being exposed to oxygen. The rust will add more weight to the can so it becomes heavier.
