Which mixture does not settle out or separate?

• A. formulation
• B. emulsion
• C. suspension
• D. solution

Answer: (D)

Solutions are homogeneous mixtures where the solute is dissolved in the solvent at the molecular level, so the entire mixture remains uniform and does not settle out. Because the particles are dispersed at such a small scale, there are no distinct phases that gravity can pull apart, so it stays evenly mixed over time. Salt water or sugar water are classic examples.

Emulsions consist of droplets of one liquid dispersed in another and can separate into layers without stabilization. Suspensions have larger particles that will settle out under gravity over time. A formulation is just a mixture prepared for a specific use and can be any type, but the property of not settling is most characteristic of a true solution.