Varies greatly on the car, where it is, how often it is driven, in what conditions it is kept and driven, etc.....too many variables in that to answer that question.
rust-ling
The best way to remove rust from a chrome with bodywork is to take your car to an autobody shop. They are the best people that can remove rust from chrome.
I don't think you are able to fix this rust problem, take you car to your local repair shop or car dealer. They should be able to take care of your problem and fix it for you. Hope I can help.
coke and a pipe cleaner
Car magnets doesn't cause rust.
it just pulls right off. It may take a little effort since rust due to the age of the car.
car radiators used to be made of copper, copper doesnt rust. most radiators are now made from aluminum.aluminum also does no rust
rust can dissolve the metal on ur car then ur car can fall apart and it will wreck your paint
Its fine
If you are new to the concept of car rust, http://www.dummies.com/how-to/content/how-to-protect-your-car-from-rust.html is a great article on a beginner's guide to it.
When salt and water and air combine, it accelerates the oxidation, therefore making the car rust faster :)
Copper doesn't rust