Concept:An ion achieves the configuration
2,8,8 when it has a total of 18 electrons, like the chloride ion.
Explanation:A chlorine atom has atomic number 17, so its electron configuration is
2,8,7.
When chlorine gains one electron, it forms the chloride ion
Cl−.
The total number of electrons in
Cl− is
17+1=18.
Therefore, its electron configuration is
2,8,8.
The other ions have only 10 electrons each, giving the configuration
2,8.
Answer:D.
Cl−