Q1. 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.
Explanation
The iron pillar near Qutb Minar (Gupta period, c. 375–415 CE, reign of Chandragupta II) is a remarkable testament to ancient Indian metallurgical skill. Modern analysis confirms it is rust-resistant due to high phosphorus content (0.15% P) resulting from the charcoal-based smelting process. The phosphorus reacts with moisture and oxygen to form a thin, stable iron hydrogen phosphate (misawite) passive layer that prevents further oxidation. Both A and R are correct, and R correctly explains A.
