# At the lowest molar concentration at ambient conditions which among the following surfactant will form micelles in aqueous solution ?

$(a)\;CH_{3}(CH_{2})_{15}N^{+}CH_{3}Br^{-}\qquad(b)\;CH_{3}(CH_{2})_{11} OSO_{3}^{-}Na^{+}\qquad(c)\;CH_{3}(CH_{2})_{6}COO^{-}Na^{+}\qquad(d)\;CH_{3}(CH_{2})_{11}N^{+}(CH_{3})_{3}Br^{-}$

Answer : $\;CH_{3}(CH_{2})_{15}N^{+}CH_{3}Br^{-}$
Explanation :
Greater is the size of the hydrophobic chain , less is the solubility in water and greater is the frequency of surfactant molecules to associate to form micelle . Hence $\;CH_{3} (CH_{2})_{15} N^{+}CH_{3}Br^{-}\;$ with the longest carbon chain has the lowest C .M .C