Surface tension of aqueous solutions of an anionic surfactant at 298 K: Concentration (mM): 1, 2, 4, 8, 16, 32 Surface tension (mN/m): 60, 52, 43, 35, 34.6, 34.5 The critical micelle concentration is closest to

A $32 mM$
B $8 mM$
C $2 mM$
D $4 mM$

Answer: B

Surface tension falls steadily while surfactant adsorbs at the interface and levels off once micelles begin to form. The values decrease up to 8 mM (35 mN/m) and are practically constant beyond it (34.6 and 34.5). The break is therefore near 8 mM.

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