2026 · Q25
Consider the following statements:
- 1Packaged foods are purged with nitrogen gas in order to prevent their oxidation.
- 2Tooth decay starts when pH of the mouth is lower than 5.5.
- 3The reactivity of metals decreases in the order: Mg > Fe > Zn.
Which of the statements given above is/are not correct?
General KnowledgeChemistry
- A2 and 3
- B1 and 3
- C3 only
- D1 and 2
Explanation
Packaged foods are flushed with nitrogen, an inert gas, to displace oxygen and prevent oxidation and rancidity (statement 1 true). Tooth enamel begins to demineralise below the critical pH of about 5.5 (statement 2 true). But the standard reactivity series orders the metals Mg > Zn > Fe, so the claimed order Mg > Fe > Zn (statement 3) is wrong. Only statement 3 is not correct. Note: UPSC's published key marks option D, but statements 1 and 2 are textbook-correct.