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?

Answer: (b) Both Statement II and Statement III are correct but only one of them explains Statement I

Both are true; only calcination (limestone → lime + CO₂) explains the huge emissions.

The idea

Cement gives off carbon dioxide from two sources. About 60% is chemical: heating limestone drives CO₂ out of the stone itself. About 40% is from the fuel burnt to heat the kiln to about 1,450°C. Clean energy can remove the second part but not the first, which is why cement is called a hard-to-abate sector.

Limestone + clay are ground together → Heated in a kiln to about 1,450°C → Limestone (CaCO₃) → lime (CaO) + CO₂ → Lime and clay fuse into clinker → Clinker + gypsum are ground → cement

Why the others are wrong

(a) Mixing clay is true but releases no CO₂, so it doesn’t explain I.

The trap

Statement II is true and part of the process — but it is not where the CO₂ comes from.

Also know

India is the second-largest cement producer after China. Ways to cut the emissions: replace part of the clinker with fly ash or blast-furnace slag (blended cements), use limestone calcined clay cement (LC3), and capture the CO₂ at the kiln.