Why might smaller quantities of nanoparticles be effective in applications?

The correct option is They have a high surface area to volume ratio. This answer is correct because it matches the approved learning objective to (chemistry only) Make order-of-magnitude comparisons for nanoscale particles in the subtopic Sizes of particles and their properties.

The correct option is They have a high surface area to volume ratio. They have a high surface area to volume ratio is correct because it directly supports the approved learning objective to (chemistry only) Make order-of-magnitude comparisons for nanoscale particles. This belongs to the subtopic Sizes of particles and their properties within Bulk and surface properties of matter including nanoparticles (chemistry only), so the explanation must stay tied to that curriculum context. The other options are incorrect because they either do not answer this learning objective, use a vague statement, or move away from Sizes of particles and their properties.