Which of the following best defines a solution?

A solution is best defined as a uniform mixture where one substance (the solute) is completely dissolved in another substance (the solvent), resulting in a single-phase homogeneous mixture. In the context of this question, the correct answer highlights that a solution can consist of solids, liquids, and gases dissolved in a liquid, which accurately reflects the broad definition in chemistry.

Solutions are characterized by their uniform composition, meaning that the solute is evenly distributed throughout the solvent and cannot be distinguished from it, which aligns perfectly with the definition provided in the correct answer. This understanding is foundational in various fields, including medicine, where the preparation and administration of medications often require solutions to ensure proper dosage and efficacy.

The other options do not capture the essence of what constitutes a solution accurately. For example, a mixture containing solid particles dispersed in oil refers to a colloidal system rather than a solution, which involves full dissolution. Likewise, a combination of liquids only does not encompass the possibility of solids or gases being part of a solution. Lastly, a method of drug delivery using aerosols describes a delivery system rather than the chemical composition of a solution. Thus, the correct answer represents the most comprehensive and accurate definition of a solution.