UPSC Prelims 2025 Q50: Environment & Ecology – Pollution & Waste Management
- (a) Both Statement II and Statement III are correct and both of them explain Statement I
- (b) Both Statement II and Statement III are correct but only one of them explains Statement I
- (c) Only one of the Statements II and III is correct and that explains Statement I
- (d) Neither Statement II nor Statement III is correct
Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I
Explanation
Activated Carbon Properties:
| Property | Mechanism | Verdict |
|---|---|---|
| II - Large surface area + heavy metal adsorption | Porous structure (~500-2,000 m2 per gram); surface chemistry binds heavy metals and organic pollutants | TRUE |
| III - Synthesised from agricultural waste | Made from coconut shells, rice husk, sugarcane bagasse - cheap, scalable, widely practiced commercially | TRUE |
Statement I: TRUE.
Activated carbon is a highly effective, widely used tool to remove pollutants from effluent streams and remediate industrial contaminants.
Statement II: TRUE - explains Statement I because its enormous surface area is what makes adsorption of heavy metals and organic pollutants possible.
Statement III: TRUE - explains Statement I because synthesis from cheap agricultural waste makes it accessible and scalable for industry.
Both II and III explain why activated carbon is such an attractive pollution control tool.
Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I.
Why each option is right or wrong
- (a) CORRECT. Both Statement II (large surface area enabling heavy metal adsorption) and Statement III (synthesis from carbon-rich agricultural waste) are accurate and both directly explain why activated carbon is effective (Statement I).
- (b) Incorrect. Both statements explain Statement I — not just one. Surface area explains the mechanism; waste synthesis explains scalability and cost-effectiveness.
- (c) Incorrect. Both Statements II and III are factually correct.
- (d) Incorrect. Both statements are well-supported by materials science and environmental engineering.
Key point
Activated carbon = large surface area (~1,000 m²/g) → strong adsorption of pollutants and heavy metals. Made from carbon-rich agricultural waste (coconut shell, rice husk).
Remember
Activated carbon = huge surface area → adsorbs pollutants. Made from agricultural waste like coconut shells and rice husk.
Common mistakes
- Confusing adsorption (molecules stick TO surface) with absorption (molecules enter INTO bulk material). Activated carbon works by ADSORPTION on its vast internal surface area.
- Not knowing the surface area scale — 1 gram of activated carbon has ~500–2,000 m² of internal surface, equivalent to several tennis courts.
- Thinking activated carbon requires synthetic or industrial precursors. It is most commonly made from agricultural waste — coconut shells, rice husk, bamboo — making it a circular economy product.
Exam tip
Adsorption vs Absorption: Ad = onto surface (activated carbon, silica gel). Ab = into bulk (sponge, desiccant). Activated carbon from waste = circular economy + water treatment. Frequently tested in environment and surface chemistry.
Sources
- NCERT Class XII — Chemistry (Surface Chemistry — Adsorption)
- Central Pollution Control Board — Water Treatment Technologies
- IIT Research — Activated Carbon from Agricultural Waste