Bohr proposed his postulates to rescue the nuclear atom from collapsing. Which of the following claims about an electron in a hydrogen atom agree with those postulates?

• I. The electron can occupy only certain orbits, called stationary states.
• II. In those orbits its angular momentum is a whole-number multiple of h/2π.
• III. While moving in a stationary orbit it radiates energy continuously, because it is accelerating.
• IV. It emits a photon of energy hν = Eᵢ − E_f when it jumps from a higher to a lower orbit.