According to Bohr's model of the atom, in which orbits can electrons revolve around the nucleus?

Niels Bohr proposed that electrons do not just fly anywhere around the nucleus. Instead, they revolve in specific, non-radiating circular paths known as discrete orbits or energy levels. While revolving in these discrete orbits, electrons do not radiate energy. An electron only gains or loses energy when it jumps from one discrete orbit to another involving absorption or emission of a photon. For most atoms, the outermost shell is considered stable when it has 8 electrons. This 'movement' of electrons to achieve 8 by sharing or transferring is what causes chemical reactions.