In the process of rusting iron, _____________ coloured powder is coated on iron.

4Fe + 3O₂ + 2H₂O$\underset{ }{\to }$ 2Fe₂O₃.H₂O

When iron metal is exposed to air for a long time, it oxidises and forms a reddish-brown colour iron oxide on its surface. This red-brown substance is known as rust, and the process of forming rust is known as rusting.