the colour changes iron nail acquires a brown coating of copper as a result of the displacement reaction in which iron has dispaced copper from copler sulphate solution .this solution becomes light green .fe(s)+cuso4=feso4+cu

Introduction:
When iron nails are put into copper sulphate solution, a chemical reaction occurs. This reaction involves the displacement of copper ions by iron atoms, resulting in the formation of iron sulphate and copper metal. The process can be explained in detail as follows:

1. Formation of Copper Sulphate Solution:
Initially, a solution of copper sulphate is prepared by dissolving copper sulphate crystals in water. The copper sulphate dissociates into copper ions (Cu2+) and sulphate ions (SO42-).

2. Interaction between Iron Nails and Copper Sulphate Solution:
When iron nails are placed in the copper sulphate solution, a redox reaction takes place. The iron atoms from the nails react with the copper ions in the solution.

3. Redox Reaction:
The redox reaction involves the transfer of electrons between the iron and copper ions. The iron atoms lose electrons and are oxidized, while the copper ions gain electrons and are reduced.

4. Oxidation of Iron:
The iron atoms on the surface of the nails lose two electrons each to form iron(II) ions (Fe2+). This process is represented by the following equation:
Fe(s) - 2e- -> Fe2+(aq)

5. Reduction of Copper:
Simultaneously, the copper ions in the solution gain two electrons each to form copper metal. This process is represented by the following equation:
Cu2+(aq) + 2e- -> Cu(s)

6. Formation of Iron Sulphate:
As the iron nails continue to react with the copper sulphate solution, iron(II) ions combine with sulphate ions to form iron(II) sulphate. This compound remains dissolved in the solution.

7. Appearance of Copper Metal:
As the copper ions are reduced to copper metal, a reddish-brown layer of copper gradually deposits on the surface of the iron nails. This is due to the displacement of copper ions by iron atoms.

Conclusion:
In summary, when iron nails are placed in copper sulphate solution, a redox reaction occurs. The iron nails are oxidized, forming iron(II) ions, while the copper ions in the solution are reduced to copper metal. This reaction results in the formation of iron sulphate and the deposition of copper metal on the surface of the nails.