# Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient condition is : -

1. A

${\mathrm{CH}}_{3}{\left({\mathrm{CH}}_{2}\right)}_{15}{\mathrm{N}}^{+}{\left({\mathrm{CH}}_{3}\right)}_{3}{\mathrm{Br}}^{-}$

2. B

${\mathrm{CH}}_{3}{\left({\mathrm{CH}}_{2}\right)}_{11}{\mathrm{OSO}}_{3}^{-}{\mathrm{Na}}^{+}$

3. C

${\mathrm{CH}}_{3}{\left({\mathrm{CH}}_{2}\right)}_{6}{\mathrm{COO}}^{-}{\mathrm{Na}}^{+}$

4. D

${\mathrm{CH}}_{3}{\left({\mathrm{CH}}_{2}\right)}_{11}{\mathrm{N}}^{+}{\left({\mathrm{CH}}_{3}\right)}_{3}{\mathrm{Br}}^{-}$

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### Solution:

It may also be noted that the critical concentration for micelle formation decreases with increase in the molecular weight of the hydrocarbon chain of surfactant.
Here the two anions that are formed are in case of "B" (i.e. CH3 (CH2)11 ${\mathrm{OSO}}_{3}^{-}$) and "C" (i.e. CH3 (CH2)6 CO$\stackrel{\mathrm{_}}{\mathrm{O}}$) The molecular weight of hydrocarbon chain is more in case of "B" so it has lower value of critical concentration for micelle formation in aqueous solution.

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