When a glass rod is rubbed with silk, the rod becomes positively charged (option B). This happens due to the transfer of electrons between the two materials. Glass tends to lose electrons easily, while silk has a higher affinity for electrons. When they are rubbed together, electrons are transferred from the glass rod to the silk. As a result, the glass rod is left with a deficiency of electrons, which makes it positively charged. The silk, having gained those electrons, becomes negatively charged. This process of charging by friction demonstrates the principle of electron transfer between materials with different tendencies to gain or lose electrons. This transfer creates a static charge on both objects, with the glass rod ending up positively charged due to the loss of electrons.