Question

When the dispersed phase is a liquid and the dispersion medium is a gas, then the colloidal system is referred to as a:
A.Smoke
B.Emulsion
C.Aerosol
D.Gel

Answer 1

Hint: Fog and mist are very good examples of colloidal solutions whose dispersed phase is a liquid and their dispersion medium is a gas. With these examples in mind, think of how such colloidal systems are classified and what their name is according to surface chemistry.

Step-by-Step Solution:
Let us first define what colloidal systems really are before moving onto the answer to this particular question.
According to Encyclopaedia Britannica, a colloid is “any substance consisting of particles substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye; more broadly, any substance, including thin films and fibres, having at least one dimension in this general size range, which encompasses about to cm. ”
It further goes on to add the following about colloidal systems that may exist as dispersions of one substance in another—for example, smoke particles in air—or as single materials, such as rubber or the membrane of a biological cell.
With these definitions in mind, let us now look at the individual nature of each of the given colloidal systems.
Starting with smoke, which is a colloidal system of solid carbon particles dispersed in air. This system is one of two which is termed as aerosol.
An emulsion is a colloidal system created when two immiscible liquids are mixed with one another. Therefore, this is not the answer to the question either.
An aerosol could refer to either of two colloidal systems, which are solid in gas and liquid in gas. Therefore, we have selected one possible answer from the given options.
Since a gel is a complex fluid consisting of two or more phases typically composed of a solid dispersed in a liquid, thus we can safely conclude that the answer to this question is c) Aerosol.
Note:
Be very careful of the distinction between the two types of aerosol i.e. liquid in gas and solid in gas as while the two colloidal systems share the same name, their properties could not be anymore different from one another.