Question

how many electrons make a stable atom

Answer 1

it varies, but most atoms have 8 electrons on their outermost orbital set (shell).

Answer 2

Yes that's ryt. But as aaronq said `mostly`, there are some exceptions to this rule called as `octet rule`.

Check out htis for more info
[ \(\sf \underline{\href{https:///en.wikibooks.org/wiki/General_Chemistry/Octet_Rule_and_Exceptions#Exceptions}{Click~Here}}\) ]

Answer 3

In order to be called stable, an atom must have enough electrons to fill the valence level. An atom may loose or gain electrons to fill this level. An atom with equal electrons and protons will have no charge, which is not considered stable.