Solution:Concept: Potassium ( ) is the most reactive and platinum ( ) is the least reactive in the series. In a single displacement reaction, which only occurs when a less reactive element in a compound may be swapped out for a more reactive element, the higher ranked element in the activity series is more reactive, as we are aware.
Therefore, when silver metal is added to copper sulphate solution, no reaction takes place as silver is less reactive than that of copper and cannot displace copper from its solution.
Hence, when a piece of silver metal is added to copper sulphate solution no reaction occurs.
Hence, the correct answer is option 4.