Iron nails are dipped into blue copper sulphate solution. After some time iron nails are :

The correct answer is Option 1. This phenomenon is explained by a displacement reaction based on the reactivity series of metals.

• Chemical Reaction: Iron (Fe) is more reactive than Copper (Cu). When iron nails are placed in a blue copper sulphate (CuSO4) solution, iron atoms displace copper ions. The reaction is: Fe + CuSO4 → FeSO4 + Cu.
• Dissolution of Iron: As iron atoms leave the nail to form ferrous sulphate (FeSO4) in the solution, the iron nail effectively dissolves or undergoes corrosion, often becoming thinner and covered with a reddish-brown copper deposit.
• Colour Discharge: The characteristic blue colour of the solution is due to Cu2+ ions. As these ions are reduced to metallic copper, their concentration decreases, and the solution turns light green due to the formation of Fe2+ ions.

Options 2, 3, and 4 are incorrect because they fail to account for both the physical degradation of the nail and the chemical transformation of the solution's colour.