Why is copper more resistant than metals like iron?

Metals like Iron are said to be more electropositive than copper- that is they tend to react by losing electrons and forming positive ions. So the more electropositive they are the more vigorously they should react to form positive ions. A better method of determining the tendendency of a metal to be oxidised (i.e. lose electrons to form that positive ion) is to connect a sample of the metal in a 1M solution of its ions to a Standard Hydrogen Electrode and read its Standard Reduction Potential from the High Resistance Voltmeter. Metals can then be ordered by their SRP. Some very reactive metals like Alumio not appear to be very reactive at all because they are covered in a thin layer of their oxide, so beware!