Solutions are formed when a solute is dissolved in a solvent. The type of chemicals and compounds that act as the solute and solvent can vary greatly. As long as the mixture is homogeneous, it can be classified as a solution.
The mechanism by which the solute is dissolved in the solvent can change depending on the state of matter of the chemicals involved. Solid solutions are metallic alloys, such as bronze, and are formed when molten metals are combined in their liquid state. Gaseous solutions are most commonly formed when one gas is dissolved into another. Air is an example of a gaseous solution.
Liquid solutions are the most commonly known and used in a laboratory setting. Liquid solutions can be formed by dissolving a solid or gaseous solute in a liquid solvent or can be the result of mixing two liquids that may or may not be solutions on their own. Water is the most common solvent and is referred to as the universal solvent because of its ability to dissolve a wide variety of solutes. Solutions that involve water as the solvent are referred to as aqueous solutions and are very common in experimental and biochemical settings.