From the definition of colloid, as long as the particle size of the dispersed phase in different aggregation states is between 1 and 100 nm, a colloidal system can be formed in different states of the dispersion medium. Except for the case where both the dispersed phase and the dispersion medium are gas and cannot form a colloidal system, the remaining 8 types of dispersion systems can form a colloidal system. When the dispersion medium is solid, it is called a solid sol; when the dispersion medium is gas, it is called an aerosol; and the colloidal dispersion system with the dispersion medium as a liquid is called a liquid sol or sol.