An emulsion is a colloidal solution consisting of:
A. two solids
B. two liquids
C. two gases
D. one solid and one liquid

Hint: Colloidal dispersion or colloids are the type of particles which lie between suspensions and solutions, there are particles which come under colloids. The difference in colloids and solutions mainly lies in the difference of the particle size. The range of diameters of colloidal particles is between 1 and 1000 nanometers.

Complete step by step answer:
Let us discuss the options one-by-one to see emulsion is a combination of:
A. two solids: In this solution, solid is a dispersed phase and solid is also the dispersed medium. This type of colloidal solution is known as solid sol. The few examples of solid sol are gemstones and coloured glasses.
B. two liquids: In this solution, liquid is dispersed phase and liquid is also the dispersed medium. This type of colloidal solution is known as emulsion. The few examples of emulsion are milk and hair cream.
C. two gases: The mixture of two gases or more gases is not a colloidal solution. The combination of gases is always a homogenous mixture. This is because gases have no identity of their own and are incompressible. The molecules are so far away that there is hindrance in mixing the two.
D. one solid and one liquid: In this solution, it can be described in two ways, one in which dispersed phase is slid and other in which dispersed phase is liquid.
In this, solid is a dispersed phase and liquid is also the dispersed medium. This type of colloidal solution is known as sol. The few examples of sol are paint and cell fluids.
In other words, liquid is a dispersed phase and solid is also a dispersed medium. This type of colloidal solution is known as gel. The few examples of gel are cheese, jellies and butter.


An emulsion is a colloidal solution consisting of two liquids, which is option ‘b’.


Note: Emulsions are thermodynamically unstable because there is a tendency for a liquid/liquid system to separate and reduce its interfacial area and its interfacial energy. Most emulsions have kinetic stability or they are stable over a period of time.