Consider the following statements: 1. Canned food items are purified with nitrogen gas to prevent their oxidation. 2. Tooth decay starts when the pH of the mouth falls below 5.5. 3. The reactivity of metals decreases in the order Mg > Fe > Zn. Which of the statements given above is/are not correct?

Statement 1 is correct: nitrogen, being inert, is flushed into canned/packaged foods to displace oxygen and prevent oxidation and spoilage. Statement 2 is correct: tooth enamel begins to demineralise and decay starts when the mouth pH falls below about 5.5 due to acid production by bacteria. Statement 3 is incorrect: in the reactivity series of metals, the correct order is Mg > Zn > Fe, not Mg > Fe > Zn, since zinc is more reactive than iron. Therefore only statement 3 is not correct.