Answer:
All of the statements are correct corresponding to Bohr's model of atom.
Explanation:
The postulates of Bohr's model of atom are:
1) Electron's revolve around nucleus in stationary states with constant energy levels.
2) The angular momentum of the electrons is quantised.
3) Electron's can change their stationary states by either absorbing energy if it moves to a state of higher energy or emitting radiations if it moves to a lower stationary state from higher state.
4) While revolving in an orbit an electron does not change it's energy.