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

Ans-a

Explanation

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 1 is correct

The cement-making process can be divided into two basic steps:  

Clinker (the main constituent of cement) is first made in a kiln with gas up to 2000°C, which heats raw materials such as limestone (calcium carbonate) with small quantities of other materials (e.g. clay) to 1,450°C. During this process, known as calcination, the calcium carbonate (limestone) is transformed into calcium oxide (lime), which then reacts with the other constituents from the raw material to form new minerals, collectively called clinker. This near-molten material is rapidly cooled to a temperature of 100 – 200°C.  

Clinker is the primary component in cement and is extremely carbon-intensive, making up 90% of overall emissions from cement.

Clinker is then ground with gypsum and other materials to produce the grey powder known as cement. 

Both Statement II and Statement III are correct and both of them explain Statement I

Read: Previous Year UPSC Environment Questions (PYQs) With Explanation 2025