Question

The red curve in the figure below shows the variation in potential energy of the system (vertical axis) as a function of the distance (horizontal axis) between two atoms as they move together to form a bond. The atoms are approaching from infinite separation (far right) toward each other. The origin is taken to be $(0,0)$.
Which of the following best accounts for the change in the potential energy of the system going from Point $B$ to Point $A$?

• A. The bond is becoming stronger as the atoms approach each other
• B. As the molecules get closer, they slow down, converting kinetic energy to potential energy
• C. As the atoms get closer together, the attraction of the nucleus of each atom for the electron(s) of the other, gets stronger and stronger
• D. As the atoms get closer together, their nuclei begin to repel one another

Answer 1

The correct option is D As the atoms get closer together, their nuclei begin to repel one another

From C to B, the coming together of atoms increases attractive force and hence the potential energy decreases.

At B, the attractive force is maximum and potential energy is minimum.

Beyond B, the repulsive force between the nuclei becomes dominant and leads to increase in potential energy.