An atom of oxygen is in an excited state When an electron in this atom moves from the third shell to the second shell the energy is?

When an electron in an excited state of an oxygen atom transitions from the third shell to the second shell, it releases energy in the form of a photon. This energy corresponds to the difference in energy levels between the two shells. The emitted photon will have a specific wavelength and frequency, which can be calculated using the energy difference and the Planck-Einstein relation. This transition often leads to the emission of visible light or ultraviolet radiation, depending on the energy involved.