Explanation of why blue color of copper sulphate solution fades on adding iron fillings:

Chemical reaction:
- When iron fillings are added to a solution of copper sulphate, a redox reaction takes place.
- The iron acts as a reducing agent, while the copper ions in the copper sulphate act as the oxidizing agent.

Formation of iron(II) sulfate:
- Iron fillings react with copper sulphate to form iron(II) sulfate and copper.
- The blue color of the copper sulphate solution fades as the copper ions are reduced to copper, which is a solid and precipitates out of the solution.
- Iron(II) sulfate is formed as a result of this reaction, which is a pale green color. This change in color from blue to pale green is observed in the solution.

Reduction-oxidation reaction:
- The reaction between iron and copper sulphate is a redox reaction, where iron is oxidized to iron(II) sulfate and copper ions are reduced to copper.
- The iron acts as a reducing agent by donating electrons to the copper ions, causing them to change from Cu²⁺ to Cu.
- This transfer of electrons leads to the fading of the blue color of the copper sulphate solution.

Overall reaction:
- The overall reaction can be represented as:
Fe(s) + CuSO₄(aq) → Cu(s) + FeSO₄(aq)

Conclusion:
- The fading of the blue color of the copper sulphate solution on adding iron fillings is due to the formation of iron(II) sulfate and the reduction of copper ions to copper metal. This change in color is a result of the redox reaction between iron and copper sulphate.