Question

Why all atoms need 8 electrons to be stable but why majorly 8. Why not any other no.

Answer 1

the octale rule states that only eight electron is allow in outermost cell.

I hope you got my answer helpful

Answer 2

The orbits have a fixed energy level so according to that the eletrons are stable in it .
We can find it by a rule called bohr and bury rule 2n^2 here n is the orbit number. This rule was given by Neil Bohr.