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 vapour pressure if the system is a closed system.
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 vapour pressure if the system is a closed system.
Show answer and solution
Answer: 2
Solution
The answer is 2, meaning exactly two statements (B and D) are correct.
B is correct because molecules at the surface experience unbalanced/uneven cohesive forces — they are pulled inward and sideways but not outward, creating a net inward pull that manifests as surface tension.
D is correct because molecules at the liquid surface have higher energy and can escape into the vapour phase (in a closed system this leads to an equilibrium vapour pressure), so surface molecules are directly responsible for vapour pressure.
A is wrong because surface tension arises from unequal (not equal) forces — bulk molecules experience equal forces in all directions (hence no net force), while surface molecules do not. C is wrong because molecules in the bulk constantly move and can migrate to the surface due to thermal/kinetic energy.
B is correct because molecules at the surface experience unbalanced/uneven cohesive forces — they are pulled inward and sideways but not outward, creating a net inward pull that manifests as surface tension.
D is correct because molecules at the liquid surface have higher energy and can escape into the vapour phase (in a closed system this leads to an equilibrium vapour pressure), so surface molecules are directly responsible for vapour pressure.
A is wrong because surface tension arises from unequal (not equal) forces — bulk molecules experience equal forces in all directions (hence no net force), while surface molecules do not. C is wrong because molecules in the bulk constantly move and can migrate to the surface due to thermal/kinetic energy.
[JEE Main 2023 · 25 Jan · Shift 2]