The correct answer is: A. It will bring about chemical change in active materials.
When a battery is overcharged, the chemical reactions that produce electricity continue even after the battery is full. This can cause the active materials in the battery to break down, which can lead to a loss of capacity and even a fire or explosion.
Option B is incorrect because overcharging a battery does not increase its capacity. In fact, it can actually decrease the capacity of the battery by damaging the active materials.
Option C is incorrect because overcharging a battery does not raise the specific gravity of the electrolyte. The specific gravity of the electrolyte is a measure of its density, and it does not change when the battery is overcharged.
Option D is incorrect because overcharging a battery can cause chemical changes in the active materials, which can lead to a loss of capacity and even a fire or explosion.