The two principal ions found in body fluids are Na(+) and Cl(-).
Na(+) is the cation formed when Na loses one electron. So, given that the atomic number of Na is 11, the number of electrons of Na(+) is 11 - 1 = 10.
Cl(-) is the anion formed when Cl gains one electron. So, given that the atomic number of Cl is 17, the number of electrons of Cl(-) is 18.
Now let's do the electron configuration of each ion.
Na(+): 10 electrons =>
[tex]1s^22s^22p^6[/tex]
Cl(-): 18 electrons =>
[tex]1s^22s^22p^63s^23p^6[/tex]
