What kind of particles are involved in a suspension?

In a suspension, the key characteristic lies in the nature of the particles involved. Suspending a substance involves large particles that do not dissolve in the solvent but remain dispersed throughout it. These particles are typically visible to the naked eye, and they can eventually settle out over time due to gravity if left undisturbed. This settling behavior is an essential feature of suspensions, differing significantly from solutions or colloids, where particles can either be completely dissolved or remain suspended without settling.

In contrast to the other options, small soluble particles imply a solution where the particles are fully dissolved and not visible, and thus cannot represent a suspension. Particles that do not settle suggest a colloid or a homogeneous mixture, while the notion of completely dissolved particles again refers to solutions rather than suspensions. Therefore, the correct response highlights the presence of large particles that can eventually settle, making it distinctly characteristic of suspensions.