Rust is oxidized iron (aka Ferric Oxide, or FeO2), or iron that has been exposed sufficiently to oxygen. It can take anywhere from hours to form in a damp or wet environment, to years in a dry one.
If they are an alloy, they will eventually rust.
How long will it t take a quarter to rust in fresh water
a long time
It depends on the quality of the nail. If it is painted it Amy take long to rust. In general it may take a month or so for the nail to rust.
a week it take or two
5 months
50 years
A very long time. Longer than you probably have.
Metals do not decompose. They rust. In a way, you can consider rust a metal;s form of decomposition, but not really.... Actually, only iron rusts. Many metals are oxidized which results in rust, patina, etc. And the length of time varies with environmental conditions and the type of metal.
Aluminum does not rust. Alumininum can also be anodized to keep it from corroding when salt and other contaminats get on it.
Copper does not rust; it develops a greenish film called patina when exposed to air and moisture. The formation of patina can take several years, depending on the environmental conditions.
a few weeks