Question

octet rule valid for which molecules with reasons

Answer 1

the atoms of these elements are found to possess 8 electrons of their outermost shell. the condition is called octet and the resultant electronic configuration is called octet configuration... it is only valid for the noble gases as it lets them become stable and not combine with other elements

Answer 2

OCTET RULE is valid for each molecule, except nearby elements of Helium.

Because, each element's atom (except atoms of nearby elements of Helium) has the tendency to have 8 electrons in its valence(outermost) shell.

But, nearby elements of Helium have the temdency to have 2 electrons in the outermost shell of their atoms, which is against The Octet Rule..

Thus, All the elements of Periodic Table ( except H, He, Li, Be, B ) follow the Octet Rule.

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Hope it was helpful