The number of electrons undergoing the trasition

The nuclear charge of the atom

the difference in the energy of the energy levels involved in the transition

the velocity of the electron undergoing the transition

ns² np³

ns² np⁴

ns² np⁵

ns² np⁶

Na < Mg > Al < Si

Na > Mg > Al > Si

Na < Mg < Al < Si

Na > Mg > Al < Si

it reflects the sequence of filling the electrons in the order of sub-energy level s, p, d and f

it helps to predict the stable valency states of the elements

it reflects trends in physical and chemical properties of the elements

it helps to predict the relative ionicity of the bond between any two elements