Q.Answer the following question.
Write postulates of Bohr's Theory of hydrogen atom.

Postulate 1. The electron in a hydrogen atom can move around the nucleus only in one of several fixed circular paths of definite radius and energy, called orbits, stationary states, or allowed energy states, arranged concentrically in order of increasing energy.

Postulate 2. The energy of an electron in a given orbit does not change with time; the electron moves from a lower to a higher stationary state only by absorbing exactly the required energy, and from a higher to a lower state by emitting energy — and this energy change is always a discontinuous jump.

Postulate 3 (Bohr's frequency rule). When a transition occurs between two stationary states differing in energy by $\Delta E$, the frequency of the absorbed or emitted radiation is $\nu = \frac{E_2-E_1}{h}$, where $E_1,E_2$ are the lower and higher state energies. …

• Omitting the angular-momentum quantisation postulate (postulate 4), which is easy to miss since it is presented alongside a supporting 'angular momentum' aside box. …