Question

Assertion :Micelles are formed by surfactant molecules above the critical micellar concentration (CMC). Reason: The conductivity of a solution having surfactant molecules decreases sharply at the CMC.

Read the above assertion and reason and choose the correct option regarding it.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

Micelles may be defined to be aggregates of long- chain diphilic surfactant molecules or ions formed spontaneously in their solutions at a definite concentration. The latter depends on the nature of the polar group and especially on the length of the molecule chain. Micelles can be characterized by the aggregation number (the number of molecules in a micelle) and the micellar mass (the sum of the molecular masses of the molecules forming a micelle).
Micelles form by the cooperative binding of monomers to one another at concentrations exceeding a rather narrow region called the critical micellization concentration (CMC). The latter is the concentration of a surfactant at which a large number of micelles form in its solution that have been in thermodynamic equilibrium with the molecules (ions), and a number of properties of the solution sharply change.
Also, conductivity of a solution having surfactant molecules decreases sharply at the CMC.