Reactivity Series: Iron in Zinc or Copper: Which Rusts Less?

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There are two test tubes with a piece of iron soaked in water in each of them. One piece of iron has a coating of zinc while the other has a coating of copper. The question is that in which test tube is the iron least likely to rust and the answer key states that it is the piece of iron with the zinc. However, shouldn't the iron with copper be least likely to rust since zinc is more reactive than Copper so it will have a higher chance of getting oxidised and forming a solid compound, thus exposing the Iron inside? Any help is greatly appreciated. Thanks.
 
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It is not about exposing the iron, it is about galvanic cells that form. Assume that iron is all the time in contact in water and try to analyze what will happen.

You may also google for sacrificial anode.

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