Why does a charged glass rod attract a piece of paper?

Paper is a dielectric, so when a positively charged glass rod is brought near it, atoms of paper get polarised, with centre of negative charge of atoms coming closer to the glass rod.

Therefore, force of attraction Fa between glass rod and piece of paper becomes greater than the force of repulsion Fr between the glass rod and the piece of paper. This results in attraction of the piece of paper towards the glass rod.