Answer:
Previous answer: Insulator because particles cannot pass through glass.
Correct answer: A glass rod is a good conductor because electrons are able to move freely within its region according to the law of conservation of charges. If you have done an experiment about it, you will find out that when you rub a glass rod with silk, a glass rod will be come positively charge, and this means that the electrons get transferred away to other objects, leaving that glass rod a deficit of electrons. This theory is based on the law of electrostatics.