A concentration-time graph shows a straight line with a negative slope. What does this indicate about the reaction order?

The negative slope indicates that the concentration of reactants is decreasing over time, suggesting that the reaction is first-order with respect to that reactant. This answer is anchored to Rate equations and orders (A-level only).

The negative slope indicates that the concentration of reactants is decreasing over time, suggesting that the reaction is first-order with respect to that reactant. is the best answer because it directly supports the AQA A-Level Chemistry objective to interpret concentration-time graphs. This reasoning is anchored to Rate equations and orders (A-level only) in Rate equations (A-level only), and it separates concentration-time from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.