the more oxygen present, the more rust you'll get. so, metal stored in oil is the best thing for the metal.
It depends on a variety of factors. It depends on the size and shape of the iron (how much surface area it has), if the iron is an alloy such as steel, or pure iron metal, if the iron is coated or treated with anything. It also depends a great deal on the environment the iron is in. Is the iron in contact with water or water moisture? Is the iron in contact with salt water? Is the iron in contact with oxygen from air? At what temperature is the iron?