Question

The figures (I, II, III) given below schematically represent variation of surface tension of three different aqueous solutions with increasing concentration of each of the solutes (surfactant, sodium chloride, and n-propanol). Match the figures with appropriate solutes and choose the correct option. 

• A. I – surfactant, II – sodium chloride, III – n-propanol
• B. I – sodium chloride, II – n-propanol, III – surfactant
• C. I – surfactant, II – n-propanol, III – sodium chloride
• D. I – n-propanol, II – sodium chloride, III – surfactant

Hint:

Surfactants reduce surface tension, sodium chloride increases it, and alcohols like n-propanol decrease surface tension as concentration increases.

Answer 1

The Correct Option is D

Step 1: Understanding the behavior of solutes.
- Surfactants: Increase the surface area by reducing surface tension initially as concentration increases and then level off after a critical concentration (Critical Micelle Concentration).
- Sodium chloride: As concentration increases, surface tension typically increases due to the ionic nature and interaction with water molecules.
- n-Propanol: Surface tension decreases with increasing concentration as it reduces hydrogen bonding between water molecules.
Step 2: Matching the figures.
- Figure I: Corresponds to n-propanol because the surface tension decreases continuously with concentration.
- Figure II: Corresponds to sodium chloride because surface tension increases with increasing concentration.
- Figure III: Corresponds to surfactant because the surface tension decreases initially and then levels off.
Step 3: Conclusion.
The correct match is I – n-propanol, II – sodium chloride, III – surfactant.
Final Answer: \[ \boxed{\text{I – n-propanol, II – sodium chloride, III – surfactant}} \]