Question

Is it a chemical reaction or physical change?
A shiny gray iron nail falls into a bucket of water. A few days later, the surface of the nail is covered in a dull, crusty, reddish-brown solid

Answer 1

This is a chemical reaction. The iron in the nail has reacted with the water and oxygen in the air to form iron oxide, which is the reddish-brown solid coating the surface of the nail. This process is known as rusting.