A formulation consisting of solid particles dispersed in a liquid is best described as a:

• A. Emulsion
• B. Solution
• C. Suspension
• D. Dispersion

Answer: (C)

Solid particles dispersed in a liquid form a suspension. In a suspension, the solid does not dissolve but remains as distinct particles within the liquid, and you can often see the particles with the naked eye or a microscope. Over time they tend to settle out under gravity unless the mixture is kept stirred or stabilized. This is different from a solution, where the solute dissolves at the molecular level; from an emulsion, where droplets of one liquid are dispersed in another immiscible liquid; and from the broader term dispersion, which can refer to various colloidal systems. So for solid particles just dispersed in a liquid, the descriptor that fits best is suspension.