Question

iron can displace copper from copper sulphate but cannot displace zinc from zinc sulphate

Answer 1

Zinc metal is more reactive than the copper. Moreover, it is placed on the top of the reactivity series. This is why, zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution. Copper being placed below zinc cannot displace it from zinc salts.

Answer 2

that's because zinc is more reactive than copper and iron