Question

Which of the following is an example of gel?
${\text{A}}{\text{.}}$ Cold cream
${\text{B}}{\text{.}}$ Cheese
${\text{C}}{\text{.}}$ Milk
${\text{D}}{\text{.}}$ Glass

Answer 1

Hint- Here, we will proceed by defining the colloidal solution. Then, we will classify colloidal solutions on the basis of physical states of both dispersed phase and dispersion medium along with examples of each case.

Step-By-Step solution:
Colloidal Solution- A heterogeneous mixture in which the minute particles of one substance (either in solid, liquid or gaseous state) are dispersed in another substance, called the dispersion medium (either in solid, liquid or gaseous state).
On the basis of the physical state of the dispersion medium and that of the dispersed phase, colloidal solutions can be classified into Solid sols, Sols, Solid Aerosol, Gel, Emulsion, Aerosol, Solid Foam and Foam.
Solid sols: These are the type of colloidal solutions in which both the dispersed phase and dispersed medium are in their solid state. Some of the examples of solid sols are alloys, glass, etc.
Sols: These are the type of colloidal solutions in which the dispersed phase is in its solid state whereas the dispersed medium is in its liquid state. Some of the examples of sols are paints, inks, etc.
Solid Aerosol: These are the type of colloidal solutions in which the dispersed phase is in its solid state whereas the dispersed medium is in its gaseous state. Some of the examples of solid aerosol are smoke, dust, etc.
Gel: These are the type of colloidal solution in which the dispersed phase is in its liquid state whereas the dispersed medium is in its solid state. Some of the examples of gels are curd, cheese, butter, etc.
Emulsion: These are the type of colloidal solution in which both the dispersed phase and the dispersed medium are in their liquid state. Some of the examples of emulsion are milk, cold cream, oil in water, etc.
Aerosol: These are the type of colloidal solution in which the dispersed phase is in its liquid state whereas the dispersed medium is in its gaseous state. Some of the examples of aerosols are mist, fog, clouds, etc.
Solid Foam: These are the type of colloidal solution in which the dispersed phase is in its gaseous state whereas the dispersed medium is in its solid state. Some of the examples of solid foam are cake, bread, etc.
Foam: These are the type of colloidal solution in which the dispersed phase is in its gaseous state whereas the dispersed medium is in its liquid state. Some of the examples of sols are soap lather, soda water, etc.
Therefore, cheese is an example of gel.
Hence, option B is correct.

Note- There does not exist any colloidal solutions with both the dispersed phase and the dispersion in their gaseous states because the dispersed phase is already at the molecular level and disperses evenly throughout the dispersing medium. It is completely homogeneous at the molecular level and hence it is a homogeneous solution.