Q. How are electric charges produced by friction(or rubbing) ? Explain it by taking  an example on the basis of movement of electrons.

When a conductor or material is rubbed against another suitable object, there is a transfer of charges between them due to friction. The body which gains electrons on rubbing becomes negatively charged, and the body which loses electrons on rubbing becomes positively charged.

Example: 
When a glass rod is rubbed with silk, electrons from the glass rod are transferred to silk. This is because the electrons are less tightly bound in glass than in silk. Thus, glass becomes positively charged due to loss of electrons and silk becomes negatively charged due to gain of electrons.