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

The correct answer is (b) Both Statement II and Statement III are correct but only one of them explains Statement I.

Explanation

Statement I: Correct. This is a well-established fact. The cement industry is a significant source of global carbon dioxide ([latex]CO_2[/latex]) emissions. Estimates vary, but it’s widely cited as being responsible for 7% to 8% of total global [latex]CO_2[/latex] emissions, which is “more than 5%”.
Statement II: Correct. This is a correct description of the cement manufacturing process. The primary raw materials for cement are a mixture of limestone (rich in calcium carbonate, [latex]CaCO_3[/latex]) and clay or shale (rich in silica, [latex]SiO_2[/latex], alumina, and iron oxide). These are ground and mixed before being fed into a kiln.
Statement III: Correct. This statement describes the core chemical reaction of cement production, known as calcination. Inside the kiln, at very high temperatures, the limestone ([latex]CaCO_3[/latex]) is converted into lime ([latex]CaO[/latex]), which is the principal component of clinker. The chemical reaction is: [latex]CaCO_3 \text{ (limestone)} \rightarrow CaO \text{ (lime)} + CO_2 \text{ (carbon dioxide)}[/latex]

Evaluating the Relationship

Why are emissions so high (Statement I)? There are two main reasons:
1. Process Emissions: The chemical reaction in Statement III releases enormous amounts of carbon dioxide that was chemically stored in the limestone. 💨
2. Energy Emissions: An immense amount of energy is needed to heat the kiln, which is typically generated by burning fossil fuels.
Does Statement II explain Statement I?No. Statement II just lists the ingredients. While true, it doesn’t explain why combining them causes emissions.
Does Statement III explain Statement I?Yes. Statement III describes the calcination process, which is the direct chemical source of about 50-60% of the cement industry’s total [latex]CO_2[/latex] emissions.

Therefore, both Statement II and Statement III are correct facts, but only Statement III provides a direct explanation for the high emissions mentioned in Statement I.