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UPSC Prelims 2025, Question 50

The concept being tested: Activated carbon — adsorption properties for heavy metal removal.

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. Which one of the following is correct in respect of the above statements?

Options

  1. ABoth Statement II and Statement III are correct and both of them explain Statement ICorrect answer
  2. BBoth Statement II and Statement III are correct but only one of them explains Statement I
  3. COnly one of the Statements II and III is correct and that explains Statement I
  4. DNeither Statement II nor Statement III is correct

The answer: Both Statement II and Statement III are correct and both of them explain Statement I

Activated carbon owes its pollutant-removal power to its intensely porous structure, carbonised and then activated with steam, carbon dioxide, or chemical agents such as phosphoric acid and zinc chloride, to create surface areas that commonly exceed five hundred to a thousand square metres per gram. This vast surface, studded with oxygen-containing functional groups such as carboxyl and hydroxyl, adsorbs heavy metal ions like lead, cadmium, chromium and mercury through physisorption, ion exchange and surface complexation. That mechanism is Statement II, and it explains why activated carbon is good at removing pollutants. Separately, activated carbon can be produced cheaply from carbon-rich wastes such as rice husk, coconut shell, sugarcane bagasse and sewage sludge. That is Statement III, and it explains why activated carbon is attractive, since waste becomes a low-cost adsorbent. Both statements are factually correct, and together they justify the twin claims made in Statement I.

What UPSC was testing

UPSC's three-statement causal format tests two separate things at once: whether Statement II and Statement III are factually true, and whether they actually explain Statement I. Aspirants who stop at verifying the facts without checking that II accounts for 'good' and III accounts for 'attractive' can mistakenly pick an option that concedes both facts but denies the explanatory link.

How often this comes up

This concept has appeared 8 times in UPSC Prelims General Studies Paper I between 2015 and 2025 — in 2015, 2020, 2022, 2023, 2024 and 2025.

The option-by-option autopsy for this question — why each of the other three is wrong, and which neighbouring concept each one was built from — is in the app.