Final answer:
As two atoms approach each other, d. both attractive and repulsive forces are in effect. Attractive forces are due to electron-nucleus interactions, while repulsive forces stem from electron-electron and nucleus-nucleus repulsions.
Step-by-step explanation:
When two atoms approach each other, there are both attractive and repulsive forces occurring. The attractive forces arise from the interactions between the electrons of one atom and the nucleus of another atom, while repulsive forces occur between the electrons of the two atoms and between their nuclei. For instance, dipole-dipole interactions may occur, where the positive end of one dipole is attracted to the negative end of another, resulting in attractive forces. Conversely, the repulsion is the result of the like charges of electrons or nuclei repelling each other.
In the specific case of two positively charged objects, such as metal balls, the electrostatic force between them would be repulsive according to Coulomb's Law. This principle is illustrated in Figure 10.5 (a), where the repulsive forces are visualized by outward pointing arrows.
Overall, stable equilibrium occurs when the attractive forces offset the repulsive forces. In forms of matter such as liquids, molecules are in continuous motion and hence continuously experience both attractive and repulsive interactions, but on average, attractive forces tend to dominate, leading to a stable molecular arrangement.