You have three separate glass rods, and you know one is positive, one is negative and one is neutral. You also have an electroscope that is positively charged.
How can you determine which rod is positive, negative and neutral?
I think you will be able to determine which rod is negatively charged, as that rod will cause the electroscope leaf to rise. I'm not sure how to differentiate between the positive+neutral though, as both will cause the leaf to collapse. Could you place it next to the negative rod and see which repels?
Essentially it would be great if somebody could explain the actual physics behind the situation. Why will the negative rod cause the leaf to rise and vice versa?