Mass ratio of CO2 from limestone decomposition Steps:

• Decomposition: CaCO₃ (100 u) → CaO + CO₂ (44 u).
• Mass fraction of CO₂ = 44/100 = 0.44.
• Total limestone = 1000 (cement) + 200 (lime) = 1200 million tonnes.
• Total CO₂ = 0.44 × 1200 = 528 million tonnes. Why B is correct:
• Matches the stoichiometric mass ratio (44/100) from the thermal decomposition of CaCO₃. Why the others are wrong:
• A: Accounts only for cement limestone (0.44 × 1000 = 440), omitting lime.
• C: Uses incorrect ratio like 0.55 × 1200 = 660, misapplying molar masses.
• D: Applies ratio to overstated total limestone (0.44 × 2000 = 880).

Final answer: B