When you bring two negatively charged balloons close to each other, they will repel each other due to the like charges. The electrostatic force between two like charges (in this case, two negative charges) is repulsive.
As you bring them closer, the strength of the electrostatic force increases because the force is inversely proportional to the square of the distance between the charges (Coulomb's Law). Thus, as the distance decreases, the force increases.
Therefore, the correct answer is:
The amount of the electrostatic force between the balloons will increase, and they will repel each other.