Chapter 5, Problem 44AP

The energy needed to ionize an atom of element X when it is in its most stable state is $\text{5}00{\text{ kJ mol}}^{-\text{1}}$ . However, if an atom of X is in its lowest excited state, only $120{\text{ kJ mol}}^{-\text{1}}$ is needed to ionize it. What is the wavelength of the radiation emitted when an atom of X undergoes a transition from the lowest excited state to the ground state?