Solutions: JEE Main Chemistry Question with Solution
Based on the given figure, the number of correct statement/s is/are
A. Surface tension is the outcome of equal attractive and repulsive forces acting on the liquid molecule in bulk.
B. Surface tension is due to uneven forces acting on the molecules present on the surface.
C. The molecule in the bulk can never come to the liquid surface.
D. The molecules on the surface are responsible for vapours pressure if system is a closed system.
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Hint 1 of 3
Which statement correctly describes the origin of surface tension according to intermolecular force balance?
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Step-by-step solutionView
Correct answer
Statements B and D are correct, making the total number of correct statements 2.
Option analysis
Why each option works or fails
Reviewed route
Solution
StepWorking
01given
Four statements describing the behavior of molecules in the bulk and at the surface of a liquid:
A. Surface tension is the outcome of equal attractive and repulsive forces acting on the liquid molecule in bulk.
B. Surface tension is due to uneven forces acting on the molecules present on the surface.
C. The molecule in the bulk can never come to the liquid surface.
D. The molecules on the surface are responsible for vapours pressure if system is a closed system.
02find
The number of correct statement(s).
03strategise
Analyze the microscopic origin of surface tension, molecular motion (diffusion), and vaporization:
1. In the bulk, a molecule experiences uniform attractive forces in all directions (net force is zero). Bulk molecules are not the origin of surface tension; surface tension arises due to an inward net pull on surface molecules.
2. Molecules on the surface experience an unbalanced net inward attractive force from the bulk molecules below, causing surface tension.
3. Liquid molecules are in continuous thermal motion; bulk molecules continually move to the surface against inward forces (requiring surface energy).
4. Evaporation occurs at the surface; escaping surface molecules generate vapor pressure in a closed container at equilibrium.
04execute
- Statement A: False. Surface tension is caused by unbalanced forces on surface molecules, not by the balance of forces on bulk molecules.
- Statement B: True. The unbalanced inward forces on surface molecules minimize surface area, creating surface tension.
- Statement C: False. Molecules in the bulk possess thermal kinetic energy and constantly exchange positions with surface molecules.
- Statement D: True. Evaporation is a surface phenomenon; molecules on the surface that overcome intermolecular attractions escape into the vapor phase to establish vapor pressure.
Total correct statements = 2 (Statements B and D).
✓verify
Exactly two statements (B and D) are correct according to standard physical chemistry concepts of surface phenomena and kinetic theory of liquids.
Hints that build this answer step by step
Which statement correctly describes the origin of surface tension according to intermolecular force balance?
Statement B is correct: surface tension arises from unbalanced attractive forces pulling surface molecules inward.
Are statements C and D true or false regarding liquid dynamics and evaporation?
Statement C is false (molecules continuously interchange) and Statement D is true (evaporation happens at the surface).
What is the total count of correct statements among A, B, C, and D?
Can bulk molecules really come to the surface if they are pulled from all sides?
Yes. Liquid molecules possess thermal kinetic energy and diffuse continuously. Work is done against attractive forces to bring bulk molecules to the surface, which is why creating new surface area requires surface energy.
