For an electron with a de Broglie wavelength $\lambda$, which of the following orbital circumferences within the atom would be disallowed? Select two answers.
This is College Physics Answers with Shaun Dychko. Electron orbitals only exist with a circumference that is an integer multiple of the de Broglie wavelength of the electron and so that means we can exclude anything that's not an integer times λ. So that means (a) and (c) are disallowed.