Answer 1

(a) Gold, being less reactive than copper, cannot displace copper from copper sulphate solution and hence, no reaction occurs.

(b) Copper reacts with copper sulphate to form copper and copper sulphate solution. So, practically no reaction occurs between them.

(c) Zinc is more reactive than copper and hence, displaces copper from its solution to form zinc sulphate solution and copper metal.
   
      Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
 
(d) Mercury, being less reactive than copper, cannot displace copper from copper sulphate solution and hence, no reaction occurs.