Final answer:
A homogeneous mixture where one substance is evenly distributed within another and cannot be physically separated or distinguished is called a solution.
Step-by-step explanation:
A mixture with one substance spread out so evenly in another substance that you cannot tell the two substances apart is called a solution. This is a homogeneous mixture that appears clear and in which the dissolved species, such as molecules or ions, are uniformly distributed throughout the solvent. Examples of solutions include saltwater in an aquarium or a solution of salt dissolved in water. In contrast to suspensions, which are heterogeneous mixtures where particles can settle out over time, or colloids, which contain larger particles that remain dispersed, a solution has a uniform composition throughout and does not allow the substances to separate upon standing. A solution like air or coffee without milk cannot have its components seen even with a microscope.