The graph above demonstrate the effect of

Correct answer: surface area on the rate of reaction.

Explanation: The curve for powdered marble rises faster and reaches the plateau sooner than marble chips. Both finish at the same final CO₂ (same amount of CaCO₃), but the powdered solid reacts faster because it has a larger surface area exposed to the acid.

• Catalyst: would speed both without changing particle size; not shown here.
• Pressure: relevant for gases, not solid–acid reactions like this.
• Concentration: would change initial rate, but the labels distinguish only particle size.