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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?
Explanation
The cement industry accounts for approximately 5-8% of global CO2 emissions[2], confirming Statement I is correct.
Statement II is correct: Limestone is the basic raw material for the cement industry[3], and limestone contains small quantities of silica, alumina, iron-oxides, phosphorus and sulphur[4]. Silica-bearing materials including clay are indeed mixed with limestone in cement production.
Statement III is also correct: Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement.[5]
However, only Statement III explains Statement I. The CO2 emitted originates from the use of fossil fuels in the high-temperature calcination step (~40% emissions) and from the chemistry of limestone (CaCO3) breaking down into lime (CaO) and CO2 (~60% emissions)[6]. The conversion of limestone to lime directly releases CO2, explaining the industry's high emissions. Meanwhile, mixing clay with limestone (Statement II) is a manufacturing practice but doesn't directly explain the CO2 emissions.
Sources- [1] https://www.sciencedirect.com/science/article/pii/S2666790823000721
- [2] https://www.weforum.org/stories/2024/09/cement-production-sustainable-concrete-co2-emissions/
- [3] NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 5: Print Culture and the Modern World > Rock Minerals > p. 111
- [4] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 7: Resources > Natural Resources of India > p. 24
- [5] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Figure 1.4 > p. 8
- [6] https://www.sciencedirect.com/science/article/pii/S2666790823000721
PROVENANCE & STUDY PATTERN
Guest previewThis is a classic 'Static-Current Hybrid'. The raw material (Limestone/Clay) and process (Calcination) are pure NCERT Class 10 Science/Geography, while the emission statistic (>5%) is a recurring theme in Climate Change reports (IPCC/IEA). The strategy is to link 'Industrial Processes' directly to their 'Environmental Footprint' rather than studying them in silos.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Do studies indicate that CO2 emissions from the global cement industry account for more than 5% of total global carbon (CO2) emissions?
- Statement 2: In cement manufacturing, is silica-bearing clay mixed with limestone as a raw material for producing cement clinker?
- Statement 3: During clinker production in cement manufacturing, is limestone (calcium carbonate) converted into lime (calcium oxide) by calcination?
- Statement 4: Does the calcination reaction that converts limestone to lime during clinker production release CO2 and thereby significantly contribute to the cement industry's carbon emissions?
- Statement 5: Does the practice of mixing silica-bearing clay with limestone in cement manufacture directly generate CO2 emissions that significantly contribute to the cement industry's overall carbon emissions?
- Directly states a numeric share for cement production in global CO2 emissions that is above 5%.
- Provides a range (5–8%) and an absolute value (~2.3 GtCO2/yr), supporting the 'more than 5%' claim.
- States a single-value estimate (8%) for the share of global CO2 emissions from cement manufacturing, which is greater than 5%.
- Specifically attributes the percentage to global cement manufacturing.
Gives an explicit example of a sectoral share (global deforestation ≈ 20% of world's CO2 emissions), illustrating that individual activities/sectors can be expressed as significant percentages of total emissions.
A student could use this sector-share framing and compare published cement-sector CO2 tonnage (from external sources) to global CO2 totals to judge whether cement exceeds 5%.
Provides national and global-emissions percentage context (India's annual emissions ≈ 7% of global emissions), showing that percentages of global emissions are a standard and meaningful way to present contribution.
Use this example of reporting (national % of global) to understand and evaluate claims about a single industry's % share (cement) by comparing industry totals to global totals.
States that CO2 emissions come from a variety of human activities and that human-related emissions have driven atmospheric increases — implying emissions inventories are disaggregated by source.
Recognize that cement is one identifiable human activity in emissions inventories; a student could consult such inventories (sector breakdowns) to see whether cement's share exceeds 5%.
Gives an example of attributing a percentage of a pollutant (black carbon) to particular countries (15–35% from China and India), showing that attributing portions of global pollutants to specific sources/regions is common and feasible.
Use the same approach to attribute CO2: combine known cement-industry emissions by country/region with global CO2 totals to estimate the industry's global percentage.
Notes the significant historical increase in atmospheric CO2 due to human activity, indicating the importance of quantifying sources and their relative contributions over time.
A student could use historical/global CO2 totals as the denominator and compare cement-sector emission time series (numerator) to assess whether the sector's share is above 5%.
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