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UPSC Prelims 2025 · Environment · Pollution Files
Consider the following statements:
- Statement I: Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries.
- Statement II: Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals.
- Statement III: Activated carbon can be easily synthesized from environmental wastes with high carbon content.
- (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
Show the answer and explanation
Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I
II explains why it is “good” (huge surface for adsorption), and III explains why it is “attractive” (cheap to make from waste).
Statement by statement
1. ✓ CORRECT It is used in water-purifier candles, industrial effluent treatment, gas masks and even for poisoning cases in hospitals.
2. ✓ CORRECT — explains I “Activation” opens up millions of tiny pores. One gram can have 500–1,500 m² of surface, and pollutants such as heavy metals, dyes and organic chemicals stick to it. This is adsorption (sticking to a surface), not absorption.
3. ✓ CORRECT — explains I It can be made from coconut shells, rice husk, sawdust or fruit peels by heating them without air and then activating the char with steam or chemicals. Cheap raw material is what makes it an “attractive” tool.
The idea
Adsorption means sticking to a surface; absorption means soaking in, like water into a sponge. Activated carbon works by adsorption, so what matters is how much surface it has. Activation fills the carbon with tiny pores and gives it an enormous surface.
Coconut shell / husk waste → Char + activate → Huge pore surface → Pollutants stick (adsorb)
Why the others are wrong
(b) Statement I says “good AND attractive”, and each of II and III explains one half.
(c) Doubts III — assuming activated carbon needs special raw material. It is made from coconut shells, husk and sawdust.
(d) Would mean it neither has a large surface nor can be made cheaply — the two reasons it is used at all.
The trap
Statement I carries two words, “good” and “attractive”. II explains the first and III explains the second, so both explain I. Also note: adsorption, not absorption.
Also know
Biochar is char made from biomass and used mainly to improve soil; it is not necessarily activated. Reverse osmosis uses a membrane to remove dissolved salts, while UV treatment targets microbes. Activated carbon does not reliably remove every salt or germ. Its adsorption sites eventually fill, so used carbon needs regeneration or safe disposal.
🔒 Activated carbon = adsorption on a huge surface area; made cheaply from carbon-rich waste.