Solutions
A solution is a homogeneous mixture formed by two or more substances. It consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent (Figure 1). The amount of solute that can be dissolved in solvent represents the latter's solubility.
Figure 1. Example of solution. Saline water is a solution formed by salts (solutes) and water (solvent). Image source : gray fish - Unsplash/ This image has been modified from the original.
Solutions are composed of only one phase, which is typically the one of the solvent. They can be found in a liquid (e.g. sodas), gas (e.g. air), or solid state (e.g. mercury dental amalgam).
A solution does not scatter light and its particles are not visible to the naked eye.