Question

A glass rod held in hand can be charged by rubbing it with silk with a copper rod cannot be charged like this why?

Answer 1

because copper is a good conductor so the charges may transfer from the copper rod to our hands then the charge on copper rod will become zero
i dont know if it is correct or not.
but yaa it may be correct

Answer 2

Glass is an insulator which can be charged by rubbing because charges remain static on its surface. Silk is conductor which cannot be charged by rubbing because charges instantly flow towards the earth by human body or flow towards the iron from earth to make it neutral. Therefore, silk cannot be charged by rubbing.