Exp) Option b is the correct answer

The cement industry is a significant source of carbon dioxide emissions due to both the chemical reactions involved in producing clinker (the main ingredient of cement) and the burning of fossil fuels to power the production process. Specifically, calcining limestone (a primary ingredient) to produce lime (CaO) releases CO2, and burning fossil fuels to heat the kilns also contributes to emissions.

Statement I is correct: Global cement manufacturing produced 1.6 billion metric tonnes of CO2 in 2022, the latest year for which there are figures – that’s about 8% of the world’s total CO2 emissions.

Statement II is correct: Silica-bearing clay is mixed with limestone while manufacturing cement. Cement production involves mixing limestone with other materials like clay, which contains silica, along with other minerals. These materials are then processed into clinker, a key component of cement.

Statement III is correct:  In the process of making cement clinker, limestone, which is primarily calcium carbonate (CaCO3), is heated to high temperatures (1450°C or 2640°F) in a kiln. This process, called calcination, decomposes the limestone into calcium oxide (CaO), commonly known as lime, and carbon dioxide (CO2). The lime then reacts with other raw materials like clay and silica to form the clinker, which is the main ingredient in cement.

Both Statement II and Statement III are correct but only one of them (i.e. Statement III) explains Statement I:

• Statement I discusses the environmental impact (carbon emissions) of the cement industry.
• Statement III explains why the cement industry has significant carbon emissions (as mentioned in Statement I), due to the conversion of limestone to lime releasing CO2.

Source: https://www.weforum.org/stories/2024/09/cement-production-sustainable-concrete-co2-emissions/