Final answer:
When identical sphere C is placed in contact with charged spheres A and B consecutively and ends up at the midpoint between them, it experiences no net electrostatic force because it has no net charge.
Step-by-step explanation:
When sphere C is first placed in contact with sphere A, it acquires half of A's charge due to charge sharing between identical spheres. The same happens when C is then placed in contact with sphere B. Since spheres A and B originally had equal and opposite charges, sphere C ends up with no net charge after these two contacts. Consequently, when sphere C is placed at the midpoint between charged spheres A and B, it experiences no net electrostatic force, because it has no charge to interact with the charges on A and B.
The force experienced by sphere C will be F/4.
When sphere C is placed at the midpoint between spheres A and B, it is equidistant from both spheres. The force between spheres A and C will be repulsive, just like the force between spheres A and B. As per Coulomb's law, the force between two charges is inversely proportional to the distance squared between them. Therefore, since the distance between C and A is half of the distance between A and B, the force experienced by C will be one-fourth (1/4) of the force between A and B.