Solutions Solutions A solution is a single phase consisting of a mixture on a molecular level of two or more components. A solution may be a gas, a liquid or a solid. If a component forms roughly micron sized clusters it is called a colloidal suspension. Colloids include a wide range of properties and are an entire field of study.
Larger clusters are simply mechanical mixtures rather than solutions.
Under normal conditions gases can mix in any proportions as long as they do not react. A mixture of oxygen and nitrogen is stable in any proportion from pure oxygen to pure nitrogen at ordinary temperature and pressure. In a mixture of oxygen, nitrogen and argon the amount of each component can be adjusted independently. If the components react, the situation is different. A mixture of two gases that will react to form a third gas is an example where there are three species present but the concentration of each is not independent.