Answer
See the detailed answer below.
Work Step by Step
When you bring your finger near the negatively charged ball, the negative charges in the ball repel the negative charges on your finger's tip.
So the negative charges in your finger travel in the opposite direction and that polarizes your finger's tip and now it is a positively charged tip.
And hence, the negative charges in the ball and the positive charges on your finger's tip attract each other. So the ball moves toward your finger.
