For a surface molecule,

(a) The net force on it is zero.
(b) There is a net downward force.
(c) The potential energy is less than that of a molecule inside.
(d) The potential energy is more than that of a molecule inside.

 
Choose the correct alterative/s:

1. (b), (c) 2. (b), (d)
3. (c), (d) 4. (a), (d)
(2) Hint: Recall the concept of surface energy.
Consider the diagram where two molecules of a liquid are shown. One is well inside the liquid and the other is on the surface. The molecule (A) which is well inside experiences equal forces from all directions, hence the net force on it will be zero. And the molecule on the liquid surface has some extra energy as it surrounded by the only lower half side of the liquid molecules.