Five ball numbered 1,2,3,4 and 5 are suspended using separate threads. The balls (1, 2), (2,4) and (4, 1) show electrostatic attraction, while balls (2, 3) and (4, 5) showrepulsion. Therefore, ball 1 must be

I 2 3 4 5+ -    +If 1 is positively charged, then 2 should be negatively charged, then 4 should be positively charged. Now, 1 and 4 cannot attract. It means ball 1 should be neutral (2 and 4 cannot be neutral because they are showing repulsion with 3 and 5, respectively).