The correct answer is: C. 10 times greater than before.
The force between two charges is proportional to the product of their charges and inversely proportional to the square of the distance between them. This means that if the charges are doubled, the force will be four times as great. If the distance between the charges is halved, the force will be four times as great.
In this case, the charges are the same, but the distance between them is halved. So the force will be 10 times greater than before.
Option A is incorrect because the force is not 5 times smaller than before. The force is 10 times greater than before.
Option B is incorrect because the force is not 5 times greater than before. The force is 10 times greater than before.
Option D is incorrect because the force is not 25 times larger than before. The force is 10 times greater than before.