Let's say we've given an electroscope a positive charge. We then bring a positively charged rod close to, but not touching, the electroscope. What does the indicator arm on the electroscope do?

1. Nothing
2. The arm deflects even more
3. The arm deflects less

The arm deflects more. Bringing a positively charged rod close to the top of the electroscope means electrons are attracted from the arms of the electroscope to the top. With even more positive charge on the arms than before the repulsive force is stronger.

Bringing a negatively charged rod close to the positively charged electroscope makes the arm deflect less. This means you can use a charged electroscope to distinguish between positively charge objects and negatively charged objects.