A suspension is composed of which of the following?

• A. Solid in liquid
• B. Liquid in liquid
• C. Gas in liquid
• D. Liquid in gas

Answer: (A)

A suspension consists of solid particles dispersed in a liquid. The solid is the dispersed phase and the liquid is the continuous phase. Because the particles are relatively large, they do not dissolve and tend to settle out under gravity, which is why suspensions often require shaking or stabilizers to keep the solids evenly distributed. In pharmaceutics, suspensions are used for drugs that are insoluble in the vehicle, and stability is enhanced by reducing particle size, using wetting agents, and adding suspending or thickening agents to slow sedimentation and prevent caking.

If the dispersed phase were a liquid in another liquid, you’d have an emulsion. If it were gas dispersed in a liquid, you’d have a foam. If it were liquid dispersed in a gas, you’d have an aerosol.