A soap bubble is given negative charge, its radius will:
A. increase.
B. decrease.
C. remains unchanged.
D. fluctuate.

Hint: To solve this question, we have to remember that like charges repel each other and unlike charges attract each other.

Complete answer:
When the soap is given negative charge, it will look like:



The charge will be distributed uniformly over the surface of the bubble by symmetry.
As we know, they want to step much farther apart, as charges repel, the only path outward, taking with them the soap surface.
At the same point, the rise in the restored force of the soap film (surface tension) would be equal and contrary to the electrostatic force, which will result in a new (larger) radius of equilibrium.
Because of the ionic similarities, this can happen to both positive and negatively charged bubbles.
Therefore, when a negative charge is given to the soap bubble, then its radius will increase.

So, the correct answer is “Option A”.

Note:
Whether the bubble is given negative charge or positive charge, the radius will increase in both cases because when positive charge is given to it, again the charges will repel each other and this will expand the bubble and the radius will increase.