Final answer:
When identical charged spheres come in contact with a neutral sphere, the two charged spheres' charges redistribute evenly. After touching each other, their new identical charges will define the new force of repulsion between them according to Coulomb's law.
Step-by-step explanation:
The question concerns the behavior of charged spheres and their interactions according to Coulomb's law. When an uncharged sphere is brought into contact with two charged spheres one after the other, it will share its charge with them. If spheres A and B are identical and charged, bringing a neutral sphere in contact with each will result in charge distribution. Assuming no other external influences, the charge on sphere A and B after contact with the neutral sphere will be such that they each have half of the original sum of their charges. The third sphere will have no charge after contact with both spheres. The new force of repulsion between A and B will then be calculated using the new charges and Coulomb's formula F = k × (q1 × q2) / r^2.
When a neutral sphere comes into contact with sphere A with charge -5 nC and sphere B with charge -3 nC, and assuming each sphere ends up with the same amount of charge due to being identical, the redistribution results in each sphere having the average of the two charges which is (-5 nC + -3 nC)/2 = -4 nC for each sphere.
To find the number of electrons equivalent to the charge on each sphere, we use the relationship that the charge of one electron is approximately -1.602 x 10^-19 C. Thus, the number of electrons can be calculated by dividing the sphere's charge by the charge of a single electron.