Final answer:
The charge transferred to the glass rod after rubbing is -5 nC, obtained by subtracting the initial charge from the final charge.
Step-by-step explanation:
The question asks about the charge on a glass rod after it has been rubbed. Initially, an insulating rod carries a charge of +2.0 nC (nanocoulombs). After being rubbed with a material, it carries a charge of -3 nC. The change in charge is the difference between the final charge and the initial charge, which is -3 nC - (+2.0 nC) = -5 nC. Thus, a charge of -5 nC has been transferred to the rod.