UPSC » Environment & Ecology Consider the following statements

Environment & Ecology Consider the following statements

Q. 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
(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

11. निम्नलिखित कथनों पर विचार कीजिए:

कथन I:
अध्ययनों से सूचित होता है कि सीमेंट उद्योग से उत्सर्जित कार्बन डाइऑक्साइड का वैश्विक कार्बन उत्सर्जन में उसके 5% से अधिक का योगदान है।

कथन II :
सीमेंट का निर्माण करते समय चूना-पत्थर में सिलिका-युक्त मृत्तिका मिलाई जाती है।

कथन III:
सीमेंट निर्माण हेतु क्लिंकर उत्पादन के दौरान चूना-पत्थर, चूना में बदल जाता है।

उपर्युक्त कथनों के बारे में, निम्नलिखित में से कौन-सा एक सही है?

(a) कथन IIऔर कथन III दोनों सही है तथा वे दोनों कथन I की व्याख्या करते हैं
(b) कथन II और कथन III दोनों सही है किन्तु उनमें से केवल एक, कथन I की व्याख्या करता है
(c) कथन II और कथन III में से केवल एक सही है तथा वह कथन I की व्याख्या करता है
(d) न तो कथन II और न ही कथन III सही है

Correct Answer: (a)

Explanation:

Statement I is correct:

The cement industry is a significant source of global CO₂ emissions, accounting for more than 5% of total global carbon emissions.

  • During the manufacturing of cement, large quantities of carbon dioxide (CO₂) are released, both from the combustion of fossil fuels and the chemical conversion of limestone (calcium carbonate) to lime (calcium oxide).
  • This makes the cement industry one of the largest industrial contributors to global greenhouse gas emissions.

Statement II is correct:

Silica-bearing clay is mixed with limestone while manufacturing cement.

  • In the raw material preparation stage of cement manufacturing, limestone (the main source of calcium) is mixed with materials containing silica, such as clay.
  • This mixture provides the essential silicon, aluminum, and iron compounds required for the formation of cement clinker.

Statement III is correct:

Limestone is converted into lime during clinker production for cement manufacturing.

  • During the clinker production process, limestone (CaCO₃) is heated in a kiln at high temperatures, causing it to decompose into lime (CaO) and release CO₂ gas in the process.
  • This step is called calcination and is a major source of CO₂ emissions in cement manufacturing.

Relation between the Statements

  • Statement I highlights the environmental impact of the cement industry, specifically its substantial CO₂ emissions.
  • Statement II and Statement III together provide the scientific and process-based reasons for Statement I:
    • Statement II explains the materials and chemical composition involved in cement production.
    • Statement III explains the key chemical transformation (conversion of limestone to lime and release of CO₂), which is the primary reason for high carbon emissions from the cement industry.
  • Both Statement II and Statement III are correct and both of them explain Statement I, as they describe the processes and raw material usage in cement manufacturing that directly result in high CO₂ emissions.

Source :

https://www.iea.org/reports/cement