Q. Consider the following statements:
Statement I:
Studies indicate that carbon dioxide emissions from the 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
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Answer & Explanation:
✅Correct Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I
Explanation:
Statement I – Correct
The cement industry is a major contributor to global carbon dioxide (CO₂) emissions, accounting for more than 5% of total global emissions (and close to 8% according to some estimates). These emissions arise from both chemical reactions during cement production and the high energy demand of the process.
Statement II – Correct
In cement manufacturing, silica-bearing clay is mixed with limestone to form the raw material. Heating this mixture in kilns requires very high temperatures, usually achieved by burning fossil fuels. This combustion process leads to indirect CO₂ emissions, contributing significantly to the overall carbon footprint of the cement industry.
Statement III – Correct
During clinker production, limestone (calcium carbonate, CaCO₃) undergoes calcination at temperatures of around 1,450 °C, converting it into lime (CaO) and releasing carbon dioxide (CO₂) as a by-product. This chemical reaction alone accounts for about half of the total CO₂ emissions from cement manufacturing.
Why Other Options Are Incorrect
- Option (b) is incorrect because both Statements II and III explain the emissions mentioned in Statement I, not just one.
- Option (c) is incorrect because both Statements II and III are factually correct.
- Option (d) is incorrect since both Statements II and III are well-established industrial facts.