When two or more pure substances are mixed together, the result is a molecularly homogeneous mixture, the content of which might change within certain parameters. The solute and the solvent are two components (substances) in a solution. The production of a solution occurs whenever two or more chemicals are combined. Based on the amount of solvent dissolved in the solution and the solutions themselves. It can be classified into three categories. Unsaturated solution, saturated solution, and supersaturated solution are the three types. 

Unsaturated solution:

Unsaturated solutions are those in which more solute can be easily dissolved, indicating that they are not saturated. 

Saturated solution:

The saturated solution is any solution to which no additional solute may be added. 

Supersaturated solution:

The definition of a supersaturated solution is one that has more dissolved solute than is required for the preparation of a saturated solution and is made by heating a saturated solution, adding surplus solute, and then gently chilling it. Furthermore, by seeding the Supersaturated Solution with fewer solute crystals, the excess dissolved solute will crystallise. 

The generation of a fine even crop of sugar crystals, for example, is the pan boiling object. Maintaining control over the crystallisation rate during the growing process is a critical condition for achieving this goal. In general, a crystal surface that is maintained in a solution will only grow if the concentration of the solution is kept higher than the saturation concentration. Supersaturated is the term used to describe such a solution. 

Supersaturation in Phase Change (Crystallisation and Condensation):

1. Every system’s physical and chemical processes take place in the vapour melt or solution phase through the synthesis of three-dimensional 3D nuclei of a new phase, which can only happen when the medium is supersaturated.
2. The production of the nuclei is linked to a shift in the system’s free energy. Even if thermodynamically conceivable, nuclei of the new phase do not form in the homogeneous system as soon as the system becomes supersaturated.
3. The system is considered to be in a state of metastable equilibrium if it can persist in that state without achieving the equilibrium state’s minimal free energy. 
4. In other words, in such cases, nucleation of the new phase occurs after a period of time, the length of which is determined by factors such as the system’s temperature and pressure, the presence of chemical phases other than the nucleating phase, and increased supersaturation levels, which facilitate the nucleation of the new phase.
5. When the new phase nucleates instantly, however, there is always a supersaturation level. That is when the new phase emerges.
6. This supersaturation level establishes the metastable width and corresponds to the upper limit of the metastable equilibrium condition. 

Applications of supersaturated solution:

1. It is in thermodynamic equilibrium when a solution of a solid solute dissolved in a liquid solvent is saturated. To crystallise, the system’s state must be altered to a nonequilibrium state, in which the solute concentration in the solution exceeds its equilibrium concentration under the given solution circumstances. Supersaturated solutions are those that are in an out-of-equilibrium state. The simplest technique to generate a supersaturated solution is to cool it. 
2. At point A, a solution is first prepared. When chilled, this solution crosses the saturation line and becomes saturated. If it is cooled past the saturation line to point B, it will become supersaturated. However, just because a solution is supersaturated does not indicate it will crystallise right away. Metastability is a property of supersaturated solutions. This indicates that in order to complete the phase transition, a free energy barrier must be overcome. 

Conclusion:

Supersaturation research is also relevant to atmospheric research. The presence of supersaturation in the atmosphere has been known since the 1940s. When water is supersaturated, it is typical for ice lattices to form in the troposphere. Under tropospheric circumstances, water particles in a saturated state will not produce ice. Water molecules do not form an ice lattice on their own at saturation pressures; they require a surface to condense on or conglomerations of liquid water molecules to freeze. Because of these factors, relative humidities above ice in the atmosphere might exceed 100%, indicating that supersaturation has occurred.