Question

Why is the electron in an atom restricted to revolve around the nucleus at certain fixed distances?

Answer 1

An electron is restricted to move around the nucleus at restricted distances because -

-The distance at which they revolve around the nucleus is determined by their principal quantum number.

-Electrons do not gain or lose energy in these shells and revolve with constant acceleration.

Thus they keep revolving at the same distance until energy is supplied and their principal quantum number changes.