UPSC Prelims 2025 · GS Paper I

Question 50: Science and Technology

Consider the following statements :

Statement IActivated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries.
Statement IIActivated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals.
Statement IIIActivated 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?

aBoth Statement II and Statement III are correct and both of them explain Statement I

bBoth Statement II and Statement III are correct but only one of them explains Statement I

cOnly one of the Statements II and III is correct and that explains Statement I

dNeither Statement II nor Statement III is correct

AnswerThe answer is (a).

Activated carbon is carbon processed to have a very large, porous surface area, so it adsorbs pollutants and heavy metals strongly. That makes it a good, attractive tool for cleaning effluent and remediating contaminants, as Statement I says. It can also be made cheaply from carbon-rich waste such as agricultural residues, coconut shells and husks, which adds to its appeal. Statements II and III are both correct, and both explain Statement I.

I. Activated carbon is widely used to treat effluents and contaminated sites.
II. Its large surface area adsorbs heavy metals; this explains Statement I.
III. It can be made easily from carbon-rich wastes; this also explains Statement I.

How you could have got this

No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) Right: high surface area with heavy metal adsorption, and cheap synthesis from waste, both explain why it is attractive.
(b) Wrong: both II and III explain I.
(c) Wrong: both II and III are correct.
(d) Wrong: both II and III are correct.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2025, General Studies Paper I, Series A. The paper on upsc.gov.in.