Which metal will react spontaneously with Cu^2+(aq) at 25 degree celcius? between Ag, Au, Mg, and hg?

Answer 1

Here is a link to the activity series of metals and their ions.
Any metal will displace any metal ION BELOW it in the series. http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html