Question

why electrons revolving around the nucleus are not attracted by the nucleus.

Answer 1

This is nature of balanced forces.. The force with which the nucleus attracts the electrons is equal to the force of electrons to repel it.. Both cancel out and thus they keep revolving

Answer 2

because the negitive charge of the electron and positive charge of the protons is equal so they don't attract each other
other reason is that while revolving electrons don't radiate energy and so that they don't fall into nucleus