What assumptions of the Bohr theory of the hydrogen atom contradict classical physics?

Answer 1

Bohr assumed that the radius of the electron in a hydrogen atom was "quantized", that is, it has well separated values so that the electron would have to jump from one orbit to another, which would have happened continuously in classical physics. The quantization of radius resulted in a quantization of the energies of the hydrogen atom and quantization of the lines in the absorption and emission spectrum of hydrogen. The latter corresponds with the observed spectra of hydrogen and other atoms.