Answer:-
Neon is a noble gas. Neon with an electronic configuration of 2,8 has 8 electrons in it's outermost shell or valence shell.
According to the Octet theory if an element has eight electrons in it's valence shell then it is stable and does not undergo reaction. Thus Neon does not need to react and can exist freely in nature.
Sodium with an electronic configuration of 2,8,1 has 1 electron in it's valence shell. As per octet rule, it is not stable and it must lose that 1 electron to become stable.
In order to lose that 1 electron sodium must react with other substances. Hence sodium cannot exist freely in nature.
