The highest rate of production of carbon(IV) oxide can be achieved using

Correct answer: 0.10 mol⁻³ HCl and 5 g powdered CaCO₃ (Option C)

Explanation (rate factors):

• Concentration of acid: Higher [HCl] ⇒ more frequent effective collisions with CaCO₃ ⇒ faster CO₂ production.
• Surface area of solid: Powdered CaCO₃ exposes more surface than lumps ⇒ faster reaction.

All options use 5 g of CaCO₃, so the amount of CO₂ formed is the same; we want the fastest rate. The combination with the highest acid concentration and powdered CaCO₃ is therefore the fastest.

• 0.05 mol⁻³ + powdered — fast, but slower than 0.10 mol⁻³.
• 0.05 mol⁻³ + lumps — slower (lower [HCl] and small surface area).
• 0.10 mol⁻³ + powdered — fastest (correct).
• 0.025 mol⁻³ + powdered — slower due to the lowest [HCl].