A lab demonstration can be performed with #CuO# and #H_2#
#CuO(s) + H_2(g) + Delta rarr Cu(s) + H_2O(g)#
#(ii)"....an amalgam of two metals that gives a liquid is called a"# #"liquidus"#
The best demonstration of this is given by sodium metal amalgam, which has the approx. formula #NaK_(2.8)#. When you take the potassium you can sometimes stick it into the sodium chunk, and it all melts......This is not used in an undergrad lab as #NaK# alloy is mighty reactive, more so than potassium. When you do the reaction you think of the 2nd cyborg in the Terminator movies which could (improbably!) melt and reassemble itself. (No more improbable than time travel of course.........)
Sodium and potassium can also dissolve in mercury to give amalgams of various compositions.