Soap solution used for cleaning purpose appears cloudy. This is due to the fact that soap micelles can

The correct answer is B, scatter light. Soap micelles are large enough to scatter the light passing through the solution, and this scattering makes soapy water look cloudy. Soap molecules have a long hydrocarbon tail that avoids water and an ionic head that likes water. In water, many molecules cluster into tiny balls called micelles, with the tails pointing inward, where they trap oily dirt, and the heads facing outward. A micelle is far bigger than an ordinary molecule, roughly in the range of colloidal particles, so the soap solution behaves as a colloid. Particles of this size scatter light in all directions, which is the Tyndall effect, and the solution therefore looks turbid instead of clear. The same effect makes a beam of sunlight visible in a dusty room. Option A is wrong because refraction is the bending of light at a boundary between media and does not make a solution cloudy. Option C is wrong because diffraction, the bending of light around edges and slits, is not what clouds the solution. Option D is wrong because micelles do not polarise light to produce turbidity. Exam tip: cloudy soap solution, micelles, colloid, scattering of light, Tyndall effect.