When Can We Say That Atom Has No Vacancy,or the Atom

Question

When can we say that atom has no vacancy,or the atom is full?  
A) An atom's outer shell is filled with electrons
B) An atom's inner shell is filled with electrons
C) An atom's outer shell is filled with neutrons
D) An atom's outer shell is filled with protons
E) An atom's inner shell is filled with protons

Accepted Answer

An atom can be considered full or having no vacancies when its outer shell is filled with electrons, which is the most stable configuration for most atoms. The other options (B, C, D, E) are not relevant in determining whether an atom is full or not.