Question

Iron nails when left in blue copper sulphate solution becomes brownish in colour and blue colour of copper sulphate solution is converted to light green

Answer 1

This is because iron nail absorb some molecules of H2O from copler sulphate pentahydrate ( CuSO4.5H2O) and react with it to form rust of brown colour. And on loosing water from copper sulphate it turns light green ( or white on complete removal of water molecule )

Answer 2

When an iron nail is dipped in copper sulphate solution, a brown coating of copper is formed in the surface of iron and the colour of copper sulphate solution changes from blue to pale green. The reaction shows that iron is more reactive than copper because it displaces copper from the copper sulphate solution.