The example of heteropolar sol is:
A.Starch sol in water
B.Rubber sol in water
C.Protein sol in water
D.Sulphur sol

Hint:Sol is a type of colloidal suspension with the presence of solid particles in a liquid. The particles may be macromolecules or may be clusters of small molecules. Lyophobic sols are the ones in which there is no affinity between the dispersed phase and liquid. They are inherently unstable, in time the particles aggregate and form a precipitate. Lyophilic sols on the other hand are very much similar to the true solutions in which the solute molecules are large and have an affinity for the solvent. Now in the question, we have been asked about heteropolar sol. So heteropolar sols are the sols that consist of different types of polar sols.

Complete step by step answer:
We will discuss each option and check whether it is an example of a heteropolar sol or not.
-Option A: Starch sol in water. Starch sol in water: Starch forms a lyophilic sol when water is used as a dispersion medium.
-Option B: Rubber sol in water. Rubber sol in water: Since rubber does not contain polar groups it does not dissolve in water.
-Option C: Protein sol in water. Protein sol in water: Since protein contains amino acids hence, they are polar. Water is also polar and amino acids and water have different polarities hence it is a heteropolar sol.
-Option D: Sulphur sol. Sulfur sol: It is a multimolecular colloid and is not polar.

Hence, option C is the correct answer.

Note:
Colloids are very common in everyday life.
Every colloid consists of two parts that are colloidal particles and the dispersing medium.
Colloids are used as thickening agents and in the manufacture of pens and inks.