Why iron nails rust in tapwater?
One water molecule is formed from 2 hydrogen atoms and 1 oxygen atom. Rust is a chemical compound of iron and oxygen. When the nail is put in the water, a chemical reaction begins. If you have 1 iron atom and 1 water molecule, then the water molecule comes apart into one molecule of hydrogen, witch forms the bubbles and one ion(a highly reactive atom) of oxygen. Then the oxygen ion reacts with the iron atom and forms a rust molecule.