UPSC Prelims 2025 · GS Paper I

Question 31: Environment and Ecology

Consider the following statements :

Statement IStudies indicate that carbon dioxide emissions from cement industry account for more than 5% of global carbon emissions.
Statement IISilica-bearing clay is mixed with limestone while manufacturing cement.
Statement IIILimestone is converted into lime during clinker production for cement manufacturing.

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 (b).

Cement making accounts for a high share of global carbon dioxide emissions, commonly put at around 7 to 8 per cent, so Statement I holds. Limestone is crushed and mixed with silica-bearing clay, then heated in a kiln to make clinker, so Statement II holds. In the kiln, limestone (calcium carbonate) decomposes into lime and carbon dioxide, which is the largest single source of cement's process emissions. So Statement III explains Statement I, but the raw mix in Statement II does not by itself explain it.

I. Cement is a major source of global carbon dioxide emissions, above 5 per cent.
II. Limestone is mixed with silica-bearing clay as raw material; this does not explain the emissions.
III. Limestone decomposes into lime and carbon dioxide in clinker making; this 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) Wrong: only Statement III, the release of carbon dioxide from limestone, explains the emissions.
(b) Right: both II and III are correct, but only III explains the emissions.
(c) Wrong: both II and III are correct, not only one.
(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.