Consider the following statements : Statement I : Studies indicate that carbon dioxide emissions from cement industry account for more than 5% of global carbon emissions. Statement II : Silica-bearing clay is mixed with limestone while manufacturing cement. Statement III : Limestone is converted into lime during clinker production for cement manufacturing. Which one of the following is correct in respect of the above statements?
- (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 ✓ UPSC's answer
- (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
Why the answer is (b)
• Cement is responsible for roughly 7–8% of global CO2 emissions, so statement I's 'more than 5%' is correct; the question is which of II and III explains that.
• Statement II is correct: cement raw meal is limestone mixed with silica- and alumina-bearing clay, but the mixing itself releases no carbon dioxide, so it does not explain the emissions.
• Statement III is correct and explanatory: in the kiln, limestone (CaCO3) is calcined to lime (CaO), releasing CO2 as a by-product — about 60% of cement's emissions — with the rest from burning fuel to reach 1,450 °C.
• Thus both II and III are true, but only III accounts for the large carbon footprint.
• Hence option (b).
Why the other options are wrong
- (a) Both Statement II and Statement III are correct and both of them explain Statement I
- Statement II (mixing clay with limestone) does not itself release CO2 and so does not explain I.
- (c) Only one of the Statements II and III is correct and that explains Statement I
- Both II and III are correct, not just one.
- (d) Neither Statement II nor Statement III is correct
- Both II and III are correct.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.