A mixture is a combination of two or more substances that retain their individual chemical and physical properties. There are two types of mixtures: homogeneous mixtures, where the substances are evenly mixed on a small scale and cannot be seen, and heterogeneous mixtures, where the individual substances can be visually identified. A solution is a type of homogeneous mixture where one substance dissolves evenly into another, such as sugar dissolving in water, forming a mixture on a molecular scale. Not all mixtures are solutions, as solubility determines whether a substance will dissolve in another.