An electroscope is charged by touching its top with positive glass rod. The electroscope leaves spread apart and the glass rod is removed. Then a negatively charged plastic rod is brought close to the top of the electroscope, but it does not touch. What happens to the leaves?

Answer: The leaves will spread.

Explanation: Since the top of the electroscope has been touched initially by a positive glass rod, the charge on it is positive (this is charging by conduction).

By bringing a negative charged rod towards (but not touching the top) the top of electroscope means we will be charging the electroscope by induction. Charging by induction implies that an opposite charge of the conductor (negative charged rod) we are using to charge will be formed on the conductor that we want to charge (already positive charged electroscope)

In this case, our plastic rod is negative and it is brought towards the top of the electroscope (which is already positively charged), there will be an induced positive charge on the electroscope.

So we have positive charge on the electroscope by a positive rod (charging by conduction) and a positive charge from a negative rod (charging by induction) thus the leaves will spread meaning the charges are repelling based on the fact that opposite charges attract and like charges repel