Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances where one substance (the solute) is uniformly dispersed throughout another substance (the solvent) at the molecular or ionic level. Common examples include salt water (where salt is the solute and water is the solvent), air (a solution of gases), and brass (a solid solution of copper and zinc). Solutions appear as single phases—you cannot distinguish the individual components by sight—and they maintain uniform composition throughout, meaning any sample taken from the solution will have the same concentration of solute as any other sample. Solutions are classified based on the state of matter of both solute and solvent: liquid solutions are most common (like sugar in tea), but solutions can also be gaseous (air) or solid (alloys). The concentration of a solution describes how much solute is dissolved in a given amount of solvent, measured in various units like molarity (moles per liter), molality, percentage composition, or parts per million depending on the application. The formation of solutions involves physical processes where intermolecular forces between solute and solvent particles overcome the forces holding the solute particles together—this is why some substances dissolve readily in certain solvents ("like dissolves like") while remaining insoluble in others. Understanding solutions is fundamental to chemistry, biology, medicine, and countless industrial processes, from preparing intravenous fluids to manufacturing beverages and processing pharmaceuticals.