When iron corrodes in the presence of air and water, it forms hydrated iron(III) oxide, more commonly known as rust.

Here's a breakdown of the process:

* Oxygen: Oxygen in the air reacts with iron to form iron oxide.

* Water: Water acts as an electrolyte, allowing the movement of ions and speeding up the reaction.

* Electrochemical Reaction: The corrosion process is actually an electrochemical reaction, where iron acts as the anode and oxygen acts as the cathode.

* Rust Formation: The reaction results in the formation of hydrated iron(III) oxide, which is the reddish-brown substance we know as rust.

The chemical formula for rust is Fe₂O₃·xH₂O, where 'x' represents the variable number of water molecules attached to the iron oxide.