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?
Answer & explanation
Answer: (b) Both Statement II and Statement III are correct but only one of them explains Statement I
Cement is among the largest single industrial sources of carbon dioxide, about 7% of global emissions according to the International Energy Agency. Both manufacturing facts are true, but only Statement III explains the emissions: heating limestone (calcium carbonate) to make lime releases carbon dioxide directly, on top of the fuel burnt in the kiln. Mixing silica-bearing clay with limestone is simply part of the recipe.
- ✓ Statement I The International Energy Agency puts the cement sector's share of global carbon dioxide emissions at about 7%, which is well above 5%.
- ✓ Statement II Cement needs limestone plus silica and alumina, which come mainly from clay or shale; this is true but does not by itself produce the carbon dioxide.
- ✓ Statement III In the kiln, calcium carbonate breaks down into calcium oxide (lime) and carbon dioxide; this 'process emission' is the main reason cement is so carbon-intensive, so III explains I.
Remember · Cement CO2 is about 7% of global emissions (IEA); most comes from calcination (CaCO3 → CaO + CO2) in clinker making, the rest from kiln fuel.
📘 Read it in NCERT: Class 10 Science, Ch 1 (practise this chapter) · Class 10 Contemporary India – II, Ch 6 (practise this chapter)
Sources
- International Energy Agency: Cement technology roadmap plots path to cutting CO2 emissions 24% by 2050 (copy of the IEA news page) ↗ “The cement sector is the third-largest industrial energy consumer in the world, responsible for 7% of industrial energy use, and the second industrial emitter of carbon dioxide, with about 7% of global emissions.”
- NCERT Class 10 · Science, Chapter 1 “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.”
- NCERT Class 10 · Contemporary India – II, Chapter 6 “This industry requires bulky and heavy raw materials like limestone, silica and gypsum.”
Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·