Why was it necessary for Bohr to assume that a bound electron in orbit did not emit radiation?
Typically, unbound particles emit radiation when they accelerate, such as speeding up or moving in a circle. If bound electrons in orbit continuously emitted radiation due to circular motion, the energy loss would cause the electrons to move closer and closer to the nucleus until falling in. Stable atoms do not collapse; bound electrons only emit radiation when transitioning from one discrete energy state to another.
Typically, unbound particles emit radiation when they accelerate, such as speeding up or moving in a circle. If bound electrons in orbit continuously emitted radiation due to circular motion, the energy loss would cause the electrons to move farther and farther from the nucleus until they escape. Stable atoms retain their electrons; bound electrons only emit radiation when transitioning from one discrete energy state to another.
None of the above. Bohr actually assumed that a bound electron continuously emits radiation.