The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solutions of KCl, CH3 OH and CH3 (CH2)11 OSO3 –Na+ at room temperature. The correct assignment of the sketches is
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Surface tension behavior depends on solute type. Electrolytes like KCl increase surface tension linearly with concentration (graph III). Non-electrolytes like CH3OH decrease it linearly (graph II). Surfactants like CH3(CH2)11OSO3–Na+ decrease it sharply initially then plateau as micelles form (graph I).
Thus, the correct assignment is: I for surfactant, II for methanol, III for KCl.
Final Answer: I: CH3(CH2)11OSO3–Na+, II: CH3OH, III: KCl