CDS 2026 (I) General Knowledge, question 25

Topic: Chemistry

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Q25

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 5.55.5.

  3. The reactivity of metals decreases in the order : Mg>Fe>ZnMg > Fe > Zn.

Which of the statements given above is/are not correct ?

  1. (a) 2 and 3
  2. (b) 1 and 3
  3. (c) 1 and 2
  4. (d) 3 onlyCorrect answer

Solution.

Answer: (d) 3 only

  1. Only statement 3 is incorrect: the reactivity order of these metals is Mg > Zn > Fe.
  2. Statement 1 is correct: nitrogen pushes out oxygen, so the food does not oxidise.
  3. Statement 2 is correct: tooth enamel starts to dissolve when the pH in the mouth falls below 5.5.