Suppose you wanted to make a metal tank to hold copper sulfate solution. Which would be the best metal to use? Why?

I would use aluminium.

All of the listed metals are more reactive than copper, and then each of them can displace copper from copper sulfate solution. However, aluminium is coated by a protective layer of aluminium oxide, which separate aluminium metal and copper sulfate solution to avoid the occurrence of displacement reaction.

I would suggest copper.

Every other metal listed is more reactive than copper. Thus, any other choice would be inclined to reduce copper ions to copper metal. However, copper itself would have no effect.

The only metals less reactive than copper are silver, platinum and gold, which are too expensive to be practical. Mercury obviously would not work because it is liquid.