Which of the following statements are true?
A. The coagulation of lyophobic sols can be done by electrophoresis.
B. Principal emulsifying agent for W/O emulsions are proteins, soaps, gums etc.
C. Alum is used for cleaning muddy water.
D. Gelatin is added in ice cream to act as emulsifier.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, C and D only
Each statement is checked against the behaviour of colloids: how lyophobic sols are coagulated, which agents stabilise each type of emulsion, and where colloids are used.
(A) Coagulation of lyophobic sols can be done by electrophoresis — True. In electrophoresis the charged colloidal particles move to the oppositely charged electrode, lose their charge there and are precipitated.
(B) Principal emulsifying agents for W/O emulsions are proteins, soaps, gums — False. Proteins, gums and soaps stabilise O/W emulsions; for W/O emulsions the emulsifying agents are heavy metal salts of fatty acids, long chain alcohols and lampblack.
(C) Alum is used for cleaning muddy water — True. \( \ce{Al^{3+}} \) ions from alum neutralise the charge on the suspended clay particles, which coagulate and settle, leaving clear water.
(D) Gelatin is added in ice cream to act as emulsifier — True. Ice cream is a colloid; gelatin, a protein that forms a lyophilic sol, stabilises the fat-in-water emulsion and protects it, as proteins do for O/W emulsions.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Coagulation or Precipitation – “… The coagulation of the lyophobic sols can be carried out in the following ways:
(i) By electrophoresis: The colloidal particles move towards oppositely charged electrodes, get discharged and precipitated.”
Emulsions – “… For stabilisation of an emulsion, a third component called emulsifying agent is usually added. The emulsifying agent forms an interfacial film between suspended particles and the medium. The principal emulsifying agents for O/W emulsions are proteins, gums, natural and synthetic soaps, etc., and for W/O, heavy metal salts of fatty acids, long chain alcohols, lampblack, etc.”
Purification of Drinking Water – “The water obtained from natural sources often contains suspended impurities. Alum is added to such water to coagulate the suspended impurities and make water fit for drinking purposes.”