The colloidal system of solid dispersed in liquid medium is called:
(A) Aerosol
(B) Sol
(C) Gel
(D) Foam

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Hint: Colloids are basically heterogeneous in nature and can be classified based on the dispersion phase and medium.

Complete step by step answer: In colloids, one substance is evenly dispersed in another. The substance being dispersed is referred to as being in the dispersed phase, while the substance in which it is dispersed is in the continuous phase. The size of colloidal particles are 1nm to 1μm.
Major classification of colloids based on the dispersion phase and dispersion medium are given below:
(i) Sol is a colloidal suspension with solid particles in a liquid.
(ii) Emulsion is between two liquids.
(iii) Foam is formed when many gas particles are trapped in a liquid or solid.
(iv) Aerosol contains small particles of liquid or solid dispersed in a gas.
The colloidal system of solid dispersed in liquid medium is called sol.

So, the correct option is B.

Additional Information: The IUPAC definition of the colloidal state can be written as follows: “The colloidal state is the state of subdivision in which molecules or polymolecular particles having at least one dimension in the range of 1 nanometre and 1 micrometre, are dispersed in some medium”. Colloids can be prepared by mechanical dispersion, Bredig’s Arc method or by peptization. Few common day to day examples of colloids are blood, cloud and gold sol.

Note: In case of the colloidal system of liquid dispersed in a solid medium it will be called gel. Thus, interchange of dispersion phase and medium changes the colloidal system.