Which of the following statements is false?

The correct answer is Option (3) → For oil in water emulsions, long chain alcohols act as emulsifying agents

An emulsifying agent forms an interfacial film between the droplets and the medium and so stabilises the emulsion; the agent must suit the type of emulsion. Long chain alcohols are agents for water in oil emulsions, not for oil in water emulsions.

• Option (1) Refractive index of dispersed phase and dispersion medium should differ in magnitude for Tyndall effect — A true statement. The Tyndall effect is seen only when the particles are not much smaller than the wavelength of light and the refractive indices of the dispersed phase and the dispersion medium differ greatly.

• Option (2) Electrophoresis shown by lyophobic colloids is mainly due to preferentially adsorbed ions — A true statement. Sol particles move in an electric field because they are charged, and preferential adsorption of ions from the solution is the most accepted reason for that charge.

• Option (3) For oil in water emulsions, long chain alcohols act as emulsifying agents — The false statement. Long chain alcohols stabilise W/O emulsions; O/W emulsions need proteins, gums or soaps.

• Option (4) Lamp black acts as an emulsifying agent for water in oil emulsions — A true statement. Lampblack is one of the agents for W/O 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):
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.”