Question

blue colour of copper sulphate is destroyed when Iron nails are added to it​

Answer 1

Explanation:

This happens because when you add iron nail to copper solution, the iron displaces copper from its salt solution as we can see that iron is more reactive than copper from reactivity table of elements.

Hence the new salt solution i.e. Iron sulphate is formed which is green in colour, blue colour of the gets destroyed and copper gets deposited to the nail.