Graph 1 represents an emission spectrum of an antique species containing various metals ( X , Q and R ). The peaks marked as K _ are due to transition from the 2 p shell to the 1s shell, while the peak marked as L _ is due to transition from the 3d shell to the 2 p shell. In multi-electron atoms, the hydrogen atom energy expression can be used if the nuclear charge Z is replaced by (Z- ), where represents the screeni