(a) This reaction will not occur. Zinc is more reactive than copper. Copper will not be able to replace zinc from zinc sulphate solution. A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal. On the other hand, if we take copper sulphate solution and zinc, then zinc will be able to replace copper from copper sulphate solution. Hence, the above reaction will not take place.

(b) A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal. This reaction will take place. In this case, Iron is more reactive than copper. In a solution of copper sulphate, iron will react and will be able to displace copper from its solution. In this reaction, iron will change into iron sulphate and copper metal will be produced.