Bohr's hypothesis:
1) Electrons revolves round the nucleus in water orbits.
2) Orbit of the electron around the nucleus can take only some special values of radius.
3) The energy of the atom as a definite value in these orbits.
4) In this Orbits, Angular momentum (e) of the electron is integral multiple of the plank's constant h divided by 2n i.e. l=nh2n.