Copper [Cu] has 28 inner core electrons
Copper is a group 11 element with atomic number 29. It has one valence electron
Valence electron is the electron in the outermost shell and it's the number of electron an atom lose or gain to become a noble gas
Cu has four electron shells with 2,8,18 and 1 electrons in each shell respectively
The outermost shell containing just one electron .
Apart from this shell, the rest of the shells contain 28 electrons and these are regarded as the inner core electrons
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