What are the postulates of Bohr's model of an atom?

The main postulates of the theory are listed:

1. In the extra nuclear portion of an atom, the electrons revolve in well defined circular paths known as orbits.

2. These circular orbits are also known as energy levels or energy shells.

3. These have been designated as $K, L, M, N, O, \ldots$ (or as $1,2,3,4,5, \ldots$ ) based on the energy present.

4. The order of the energy of these energy shells is: $K

5. While revolving in an orbit, the electron is not in a position to either lose or gain energy. In other words, its energy remains stationary. Therefore, these energy states for the electrons are also known as stationary states.