Which of the following statements is not correct about rusting of iron?

We need to identify which statement is NOT correct about rusting of iron.

Analysis of each statement:

Statement (1): "Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off."

This is INCORRECT. While an intact tin coating acts as a physical barrier preventing contact with moisture and air, once the tin coating peels off or gets scratched, the iron underneath actually corrodes faster. This is because tin (Sn) is less reactive than iron (Fe) — tin has a higher reduction potential ($$E°_{Sn^{2+}/Sn} = -0.14$$ V) compared to iron ($$E°_{Fe^{2+}/Fe} = -0.44$$ V). Therefore, when both are exposed, iron acts as the anode and preferentially corrodes, while tin acts as the cathode. This is in contrast to zinc coating (galvanizing), where zinc being more reactive than iron, sacrificially corrodes to protect iron even if the coating is damaged.

Statement (2): "When pH lies above 9 or 10, rusting of iron does not take place."

This is correct. In highly alkaline conditions (pH > 9-10), iron forms a protective oxide layer that is stable and prevents further corrosion. This is the principle behind adding alkali to boiler water.

Statement (3): "Dissolved acidic oxides SO$$_2$$, NO$$_2$$ in water act as catalyst in the process of rusting."

This is correct. Acidic oxides dissolve in water to form acids, lowering the pH and increasing the concentration of H$$^+$$ ions, which accelerates the electrochemical process of rusting.

Statement (4): "Rusting of iron is envisaged as setting up of electrochemical cell on the surface of iron object."

This is correct. Rusting involves the formation of an electrochemical cell where iron acts as the anode (gets oxidized to Fe$$^{2+}$$) and oxygen is reduced at the cathode in the presence of water.

The correct answer is Option (1).