Aneutral copper ball is suspended by a string. a positively charged insulating rod is placed near the ball, which is observed to be attracted to the rod. why is this? 1. the ball becomes positively charged by induction. 2. the string is not a perfect conductor. 3. there is a rearrangement of the electrons in the ball. 4. the ball becomes negatively charged by induction. 5. the number of electrons i

The correct answer is:
3. there is a rearrangement of the electrons in the ball. 

In fact, the ball is made by copper, which is a good conductor, therefore its electrons are free to move on the surface of the ball. When the positively charged rod is placed near to the ball, the electrons in the ball re-arrange, in particular they are attracted from the positive charges of the rod so they move closer to it. And since opposite-sign charges attract each other, the ball is then attracted by the rod.