Step-by-step explanation:
In order to follow octet rule, there must be 2, 8, 18, 32 etc electrons in the shells of an atom.
For example, helium has 2 electrons therefore, its octet is complete. Whereas chlorine has 17 electrons, that is, its electronic distribution is 2, 8, 7. So, its octet is incomplete and hence it is not stable.
This means there must be eight electrons around each atom to fulfill the octet rule.