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RAS question

Assertion (A): The iron pillar near the Qutb Minar in Delhi, dating to the 4th–5th century CE, is still largely rust-free after 1,600 years. Reason (R): The pillar's rust-resistance is due to the high phosphorus content resulting from the ancient Indian smelting process, which forms a protective passive layer.

Correct answer: (A) Both A and R are correct, and R is the correct explanation of A.

The Gupta-period Iron Pillar in Delhi's Qutb Minar complex is more than 1,600 years old yet remains largely rust-free because phosphorus in the iron helps form a thin protective iron hydrogen phosphate hydrate layer on its surface.

  1. (A)

    Both A and R are correct, and R is the correct explanation of A

  2. (B)

    Both A and R are correct, but R is NOT the correct explanation of A

  3. (C)

    A is correct, but R is wrong

  4. (D)

    A is wrong, but R is correct

Explanation

The assertion and the reason are both correct, and the reason explains the assertion. The pillar in Delhi's Qutb Minar complex belongs to the Gupta period, around 400 CE—the fourth-fifth centuries CE—and remains relatively rust-free after more than 1,600 years. This makes it important both historically and for the study of metallurgy. In the ancient process, iron was smelted using wood charcoal, leaving it with a relatively high phosphorus content. Britannica explains that phosphate-related chemical reactions gradually form a thin iron hydrogen phosphate hydrate layer on the surface. This protective layer slows further oxidation and therefore accounts for the pillar's limited rusting.

Why the other options are wrong

  • (B) Option B is wrong because the reason is neither separate nor unrelated: the protective phosphate layer formed through phosphorus-related reactions explains the pillar's limited rusting.
  • (C) Option C incorrectly treats the reason as false, even though phosphorus-related chemical reactions and the protective layer explain the pillar's corrosion resistance.
  • (D) Option D incorrectly treats the assertion as false, whereas Britannica describes the pillar as more than 1,600 years old and relatively rust-free.

Concept

This question tests knowledge of metallurgy and technological achievements in Gupta-period India. RAS often asks about such examples because they connect cultural history and science and technology with material evidence rather than relying only on dynastic chronology.

Source

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