Which of the following occurs when an electron moves from a higher energy shell to a lower energy shell? A. A neutron is always lost. B. A proton is always gained. C. Energy is released in the form of radiation. D. The electron must be transferred to another atom.

Energy is released in the form of radiation. For an electron to move from a lower shell to a higher one, energy must be put in. This means that going from a higher shell to a lower one, it must lose energy to be in a less excited state. The electron must emit this radiation in the form of light with a wavelength equivalent to the amount of energy put in.