What type of mixture is most likely to settle if undisturbed?

The correct answer is a suspension. A suspension is a type of mixture where solid particles are dispersed in a liquid but are not dissolved. Over time, if left undisturbed, the heavier solid particles in a suspension will settle to the bottom due to gravity. This characteristic is key in distinguishing suspensions from other types of mixtures.

In contrast, a solution is a homogeneous mixture where one substance (the solute) is completely dissolved in another (the solvent), resulting in a uniform appearance that does not settle. A mixture, in general, can refer to any combination of materials that are combined but not chemically bonded, which does not specifically indicate if it will settle. An emulsion specifically refers to a mixture of two immiscible liquids where one is dispersed in the other, and while emulsions may appear cloudy, they do not settle out like a suspension does.

Therefore, suspensions are uniquely identified by their tendency to allow solid particles to settle, making them the correct choice in this scenario.