Answer: Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus.
so C would seems to be right.
Explanation: The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.
