Answer: Option (a) is the correct answer.
Explanation:
It is known that when two objects which have opposite or unlike charges come in contact with each other then they tend to attract each other.
Whereas when two objects which have same or like charges come in contact with each other then they tend to repel each other.
Therefore, we can conclude that when two plastic balls suspended by strings are placed close to each other and they have same charge then they will repel each other.
