A student plots a graph of the concentration of a reactant against time for a chemical reaction. The graph shows a curve that decreases over time. What does this indicate about the reaction rate as it progresses?

The decreasing curve indicates that the concentration of the reactant is decreasing over time, which implies that the reaction rate is also decreasing as the reactant is consumed. This is typical for many reactions where the rate slows down as the reactants are used up. This answer is anchored to Mathematical requirements.

The decreasing curve indicates that the concentration of the reactant is decreasing over time, which implies that the reaction rate is also decreasing as the reactant is consumed. This is typical for many reactions where the rate slows down as the reactants are used up. is the best answer because it directly supports the AQA A-Level Chemistry objective to plot, interpret and analyse graphs. This reasoning is anchored to Mathematical requirements in Mathematical requirements and assessment objectives, and it separates graph 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.