NCERT Solutions Curiosity Chapter 4 Activity 4.5: Let us experiment — Effect of Air and Water on Metals: Iron
Book page 49 & 50 Updated on2026-09-05
Q1.
Place all the glass bottles undisturbed at room temperature and observe the changes for 8 – 10 days. Record your observations in Table 4.3.
Answer
Each bottle is designed to allow only one condition. Fill Table 4.3 like this.
Glass Bottle
What is inside
Presence of water (Yes/No)
Presence of air (Yes/No)
Observations
A
Iron nail + silica gel, capped tightly
No
Yes
No brown deposit — the nail stays shining
B
Iron nail fully dipped in boiled and cooled water, oil layer on top, capped
Yes
No
No brown deposit — the nail stays shining
C
Iron nail partly dipped in water, bottle left open
Yes
Yes
Brown deposit appears, mostly near the water line
Bottle A is capped with silica gel (dry air), bottle B has boiled water sealed under an oil layer (no air), bottle C is open with the nail half in water.
Tip: the silica gel in bottle A soaks up moisture, the boiling drives dissolved gases out of the water in bottle B, and the oil layer stops fresh air from dissolving back in. Each step removes exactly one thing — that is what makes the experiment a fair test.
Q2.
What can you conclude from this experiment?
Answer
Conclusion: the presence of both water and air is essential for brown deposits to develop on iron.
Bottle A (air only, dry) → no deposit
Bottle B (water only, no air) → no deposit
Bottle C (air and water) → brown deposit So moist air is responsible for the brown deposit on iron objects.
This brown deposit is called rust, and the process of its formation on objects made of iron is called rusting.
Why it happens: rusting is a slow reaction between iron, the oxygen of the air and water. Take away either one and the reaction cannot start — which is exactly what bottles A and B prove.
Did you know? Rusting is not limited to iron. Copper objects grow a green coating and silver objects a black one. The general name for this gradual eating away of a metal surface by air, water or other substances is corrosion.