Solutions are formed when two or more substances are mixed on an atomic or molecular scale to form one state only. A solution can be composed of liquids, gases or solids, but the resulting solution must be one state. Sea water is a typical solution. It is formed when solid salt is dissolved in liquid water to form the liquid "salt water" solution. Muddy water is not a solution; it is a simple mixture. Solid dirt and liquid water have been mixed, but the two have not mixed on a molecular scale to form one state. The dirt remains as relatively large clumps in the mixture. Clean air is a solution of many different gases, but polluted air is not a solution. It is a mixture of larger bits of solids and liquids in the air gases.

Test for solutions
The simple test for a liquid or gas solution is to look at it. If light passes through, even if it is coloured, then the particles are very small and it is a solution. If you cannot see through it clearly and it looks cloudy or dirty, then at least some of the particles are relatively large clumps and it is a mixture, not a solution.

Solutions are physical mixtures of two or more substances, the parts of which are not chemically combined and can be separated relatively easily. For example, the salt can be separated from the water in sea water by warming the solution and evaporating off the water, leaving the solid salt behind. The salt and the water themselves are chemicals and cannot be further separated without applying chemical means.

Types of solutions
Solutions fall into different categories depending on what states are mixed and the state of the resulting solution. Some common examples are:

• Gas + gas to give a gas solution air
  
• Gas + liquid to give a liquid solution soda water
  
• Liquid + liquid to give a liquid solution alcoholic drinks
  
• Solid + liquid to give a liquid solution salt water
  
• Solid + solid to give a solid solution metal alloys

Solutes and solvents
The components of solutions are divided into two types, solutes and solvents. Generally, the solute is the substance in the lesser quantity in the solution and the solvent is the substance in the greater quantity. In sea water there is a lot more water than salt, so the water is the solvent and the salt is the solute. The solute is said to dissolve in the solvent to form the solution.