### Video Transcript

In an experiment, a student added a
sample of a solid into a solution, resulting in a chemical reaction. The student repeated the experiment
five times but changed the surface area of the solid. The graph showing how the
concentration of one of the products changes over time for each experiment is shown
below. In which experiment was the surface
area of the solid the greatest?

In the experiment in this question,
a solid was added to a solution, and the solid reacted. The concentration of a product of
this reaction was graphed over time. Each of the lines on this graph
represents the same reaction with the same mass of solid. The only difference is the surface
area of the solid. We need to figure out which of
these lines represents the experiment where the surface area of the solid was the
greatest. In a solid, only particles on the
surface can react. If we increase the surface area,
more solid particles are exposed and available to react. This means the reaction will occur
more quickly if the surface area is larger. So the experiment where the solid
had the largest surface area will also be the experiment where the reaction occurs
the fastest.

Looking at this graph, we can see
that each line reaches the same maximum value for the concentration of the product,
about 1.5 moles per liter. But each line took a different
amount of time to reach 1.5 moles per liter. The red line got there first. The pink line took the longest to
get there. In other words, the red line was
the experiment where the reaction happened the fastest and the pink line was the
experiment where the reaction happened the slowest. As we said, the fastest reaction
will correspond to the greatest surface area. So the red line represents the
experiment where the surface area of the solid was the greatest, making answer
choice (B) the correct answer.