To determine what will most likely occur as the student brings the balloons closer to each other, we need to consider the nature of the charges on the balloons.
If the balloons are charged with the same type of charge (both positive or both negative), they will repel each other. In this case, as the balloons are brought closer together, the magnitude of the electrostatic force will increase because the force is inversely proportional to the square of the distance between them.
If the balloons are charged with opposite types of charge (one positive and one negative), they will attract each other. As they are brought closer, the magnitude of the electrostatic force will also increase.
Since the question does not specify the types of charges on the balloons, both scenarios (either repulsion or attraction) would lead to an increase in the magnitude of the electrostatic force as they get closer.
Therefore, the correct answer, assuming we don't know the type of charge on the balloons, most closely aligns with option c:
c. The magnitude of the electrostatic force between the balloons will increase, and they will repel each other. (if they have the same charge)
However, if they have opposite charges, it would also increase and they would attract. So, without specific information about the charges, and focusing just on them being brought closer together, option c seems to be the most appropriate choice regarding the increase in force.