Question

Which of the following forms cationic micelles above certain concentration?

• A. Sodium dodecyl sulphonate
• B. Sodium acetate
• C. Urea
• D. Cetyl trimethyl ammonium bromide

Answer 1

The Correct Option is D

The question asks which compound forms cationic micelles above a certain concentration. A cationic micelle is formed by surfactants that have a hydrophobic tail and a positively charged (cationic) headgroup. Let's examine the options:

1. Sodium dodecyl sulphonate: This is an anionic surfactant where the sulphonate group is negatively charged, so it forms anionic micelles, not cationic ones.
2. Sodium acetate: This is a salt of acetic acid and is not a surfactant. It doesn't form micelles because it lacks a long hydrophobic tail and a charged headgroup structure typical of surfactants.
3. Urea: Urea is a small, nonionic compound that does not form micelles because it doesn't have the amphiphilic nature required for micellization.
4. Cetyl trimethyl ammonium bromide: This compound is a cationic surfactant. It has a long hydrophobic tail (cetyl group) and a positively charged headgroup (quaternary ammonium). Above its critical micelle concentration (CMC), it forms cationic micelles in solution.

The correct answer is Cetyl trimethyl ammonium bromide because it meets the criteria for forming cationic micelles.

Conclusion: The option Cetyl trimethyl ammonium bromide forms cationic micelles above a certain concentration due to its amphiphilic structure.