Final answer:
The Na⁺ ion at rest experiences no net force because the attractive electric force of surrounding electrons is balanced and cancels out.
Step-by-step explanation:
When a Na⁺ ion is at rest, the net force is nonexistent (d). This situation occurs because the attractive electric force of the surrounding electrons is equal in all directions, which cancels out the net force on the ion. When considering other forces, such as the weak nuclear force, the strong nuclear force, and the gravitational force, they are not necessarily relevant to the net electric force on the ion. For instance, the strong nuclear force does not influence electrons (d). Additionally, two positive charges, like the Na⁺ ion at rest, placed near each other on a screen would create an electric field that is strongest halfway between the charges (d), not nonexistent.