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

CO₂

NO₂

SO₂

SiO₂

PH₃

NH₃

$$CH_3^+$$

SbH₃