Consider the following statements: [Ecology]

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?

The correct option is: Both Statement II and Statement III are correct and both of them explain Statement I.

Let's analyze each statement step-by-step to understand why this option is correct:

1. Analysis of Statement I:
Statement I asserts that carbon dioxide (CO₂) emissions from the cement industry account for more than 5% of global carbon emissions. This is correct. Globally, the cement industry is one of the largest industrial contributors to carbon dioxide emissions, responsible for approximately 7% to 8% of global anthropogenic CO₂ emissions.

2. Analysis of Statement II:
Statement II states that silica-bearing clay is mixed with limestone while manufacturing cement. This is correct. The primary raw materials for cement manufacturing are calcium carbonate (typically limestone) and silica-rich materials (like clay, shale, or sand). These materials are finely ground and blended together to provide the necessary calcium, silicon, aluminum, and iron oxides for clinker formation.

3. Analysis of Statement III:
Statement III states that limestone is converted into lime during clinker production for cement manufacturing. This is correct. When the raw mix is heated in the kiln to very high temperatures (calcination), limestone (calcium carbonate, CaCO₃) thermally decomposes into lime (calcium oxide, CaO) and carbon dioxide (CO₂).

4. Linkage and Explanation:
To understand how Statement II and Statement III explain the high CO₂ emissions mentioned in Statement I, we look at the chemistry of cement production:
- Statement III describes the calcination process where limestone (CaCO₃) is converted to lime (CaO). This chemical reaction directly releases CO₂ into the atmosphere. The chemical equation for this reaction is:
$${\text{CaCO}}_3\to \text{CaO}+{\text{CO}}_2$$
This process alone contributes to about 50% to 60% of the total CO₂ emissions from cement manufacturing.
- Statement II describes mixing clay (silica-bearing) with limestone. Because these minerals must react chemically at extremely high temperatures (around 1450 °C) to form calcium silicates (clinker), a significant amount of thermal energy is required. Burning fossil fuels to heat the kiln to these temperatures generates the remaining portion (about 40%) of the cement industry's CO₂ emissions.

Therefore, both the chemical raw material mixture (Statement II) and the chemical transformation process (Statement III) are direct drivers of the massive energy consumption and carbon emissions, fully explaining Statement I.