What best describes a solution?

A solution is best described as a substance dissolved in a liquid because it specifically refers to a homogeneous mixture where the solute (the substance being dissolved) is uniformly dispersed throughout the solvent (the liquid in which it's dissolved). In a solution, the particles of the solute are so small that they cannot be seen and cannot settle out over time, allowing for a consistent composition throughout. This property is fundamental in understanding how solutions behave and how they can be applied, especially in agricultural contexts where chemicals such as pesticides must be effectively distributed within a liquid medium for proper application.

Comparatively, a mixture of solids and liquids often leads to a heterogeneous system where the components can often be separated and are not uniformly mixed. A thin film of liquid does not provide insight into the composition of a solution, as it can refer to various forms of liquid that may or may not involve solubility. Lastly, a solid particle in a liquid indicates a suspension or colloidal system rather than a true solution, which lacks the uniformity characteristic of solutions. Understanding these distinctions is crucial for anyone involved in the application of pesticides or any chemical solution.