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Q25 (CDS-I/2026) Science & Technology › Basic Science (Physics, Chemistry, Biology)

Consider the following statements: 1. Packaged foods are purged with nitrogen gas in order to prevent their oxidation. 2. Tooth decay starts when pH of the mouth is lower than 5·5. 3. The reactivity of metals decreases in the order : Mg > Fe > Zn. Which of the statements given above is/are not correct?

Result
Your answer: —  Â·  Correct: D

Explanation

Statement 1 is correct: Nitrogen is an inert gas used in food packaging to displace oxygen. This prevents the oxidation of fats and oils, which would otherwise lead to rancidity and spoilage.

Statement 2 is correct: Tooth enamel, made of calcium hydroxyapatite, is the hardest substance in the body. However, it begins to corrode (demineralize) when the pH in the mouth falls below 5.5 due to acid production by bacteria fermenting sugar particles.

Statement 3 is incorrect: According to the reactivity series of metals, Zinc (Zn) is more reactive than Iron (Fe). The correct decreasing order of reactivity for these metals is Mg > Zn > Fe. Since the question asks for the statement that is not correct, only statement 3 is the answer.

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