What is a characteristic of a solution?

A solution is a homogeneous mixture where the components are evenly distributed at a molecular level. This characteristic allows solutions to remain uniform without the need for agitation, meaning that the solute is completely dissolved in the solvent and does not settle or separate over time.

In contrast, mixtures that separate into layers or can be filtered reveal the presence of distinct phases or particles, which are typical of heterogeneous mixtures. For example, an emulsion or suspension might exhibit layering or can be separated by filtration due to differences in particle size or density. Solutions do not retain undissolved solid particles; any solid that remains is no longer considered a true solution. Thus, a key factor defining a solution is its uniformity throughout, which highlights the correctness of C as the defining characteristic of a solution.