Ascientist designs an experiment that requires two atomic particles whose only fundamental force exerted between them is the gravitational force. which combination of particles and separation distance will meet this condition?

Infinite distance; all objects in the universe.

Explanation:

In physics, there are four fundamental interactions, and the fundamental interactions include strong force, electromagnetic force, weak force and gravitational force. These forces governs how objects or particles interact and how certain particles decay.

With respect to their relative strengths, the strong force is regarded as the most powerful, followed by the electromagnetic force, the weak force, and the gravitational force.

Gravitational force and electromagnetic force operates at infinite distance. Gravitational force acts between all objects of the universe, no matter the distance/how far the body are apart.