The correct option is 2 and 3 only.
Explanation
This question illustrates a single displacement reaction governed by the Reactivity Series of metals. A more reactive metal can displace a less reactive metal from its salt solution. Iron (Fe) is placed above Copper (Cu) in the reactivity series, making it more reactive.
Statement-wise Analysis:
- Statement 1 is Incorrect: When an iron nail is immersed in copper sulphate solution, iron displaces copper. The displaced copper deposits on the surface of the iron nail, giving it a reddish-brown coating. Therefore, the nail does not retain its original silvery-grey appearance.
- Statement 2 is Correct: The aqueous solution of copper sulphate ($CuSO_4$) is blue in colour. As the reaction proceeds, copper ions ($Cu^{2+}$) are displaced by iron ions ($Fe^{2+}$). Consequently, the intensity of the blue colour fades and gradually changes to a light green colour.
- Statement 3 is Correct: The chemical reaction involved is:
$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$
The product formed in the solution is ferrous sulphate ($FeSO_4$), which is responsible for the light green colour of the solution.
Key Takeaway:
In a displacement reaction, a more reactive metal (like Iron) displaces a less reactive metal (like Copper) from its aqueous salt solution, resulting in a distinct colour change in the solution and deposition on the metal surface.