The phenomenon in which a compound exists in two or more crystalline forms is called ________________?

A. Weight
B. Valency
C. Size
D. Chemical property

A. Compound
B. Element
C. Electrolyte
D. Mixture

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent.
Air is an example of gas solution as it is an homogeneous mixture of several gases.