Which element is used for the shiny trim on cars

The correct answer is either Chrome (Chromium), or Aluminum. Unlike steel, these two don't rust easily and can be polished to be quite shiny, especially Chromium, which is why you'll always hear people who like cars talking about chrome wheels and chrome spoilers and things like that. They are not that good for bumpy or roads that are full of holes because they can bend much easier than steel so it can be expensive to maintain.