Because it is a medal
They combine to form rust. You might be able to guess from what's combining that "rust" is apparently an iron oxide.
The dissolved oxygen in the water reacts with the nail to form rust.
The chemical property that causes rust to form on a nail is oxidation. The iron in the nail reacts with oxygen in the presence of water or moisture to form iron oxide, which is commonly known as rust.
Iron present in the nail oxidizes in oxygen to form the iron oxides
You rust a nail in either salt water or in vingar that what makes a nail rust
Fe2O3 Iron Oxide time is varying but if the metal is hotter rust occurs faster.
When sodium hydroxide solution is added to a rusty nail, it reacts with the iron oxide (rust) to form soluble sodium ferrate, which helps to dissolve and remove the rust from the surface of the nail. This process is known as chemical dissolution, where the sodium hydroxide breaks down the rust into a soluble form that can be easily washed away.
If a nail is kept in tap water, it can start to rust due to the presence of oxygen and minerals in water. Over time, the nail's surface may corrode and form a reddish-brown layer known as rust.
The best solution to rust a nail is to apply a rust converter or a rust inhibitor. This will help to neutralize the rust and prevent further corrosion. Sanding the nail to remove the rust and then painting it with a rust-resistant paint can also be effective.
It either cleans the nail, or makes the nail have rust.
Most likely, the iron nail is oxidizing. The iron in the nail would then be reacting with the oxygen in the air to form rust.
Because a rusty nail still contains the same amount of iron that was present in the unrusted nail only it now contains the additonal weight of the oxygen which has combined with the iron to form rust.