When iron reacts with oxygen and water, the chemical reaction that forms is known as rust. This is considered to be corrosive for most metal elements.
The iron turns to rust (Iron Oxide).
Iron will react with water and oxygen to produce rust. Essentially water has oxygen atoms in it so as long as iron is in contact with water, it will rust.
Oxidation
Potassium react violent with water, iron react only if oxygen is present.
The iron would react with the oxygen in the water to make iron oxide, or rust.
What happens when iron and oxygen react?
The most obvious factors necessary for the corrosion of iron (or the making of rust) is water and oxygen. Iron will not rust if it is kept away from water and oxygen
Iron does not react with water because the hydrogen and Oxygen are already combined. Also Hydrogen is an Akaline metal which means no other metal could take its place.
Metal reacting with oxygen is known as oxidation. A common form of this process is found in the rusting of iron, where the iron reacts with oxygen to form iron oxide (known as rust).
Nails do not rust in water. Nails only rust in water if oxygen is present. This is because the iron in nails react with oxygen and water to form a compound called hydrated iron(III) oxide.
Pure Iron (Fe) doesn't directly react with water, but it will oxidize (rust), especially if the iron is just wet and is exposed to air a lot. I believe iron will eventually oxidize if kept completely underwater too, but as there is less free Oxygen for it to react with down there, it is a longer process.
Add some h20 and you got yourself a heap of rust
Oxygen