a) The first atom would be calcium. It has 20 electrons. If you look on the periodic table you will see that atomic number 20 coresponds to calcium. The electron configuration is (1s^2)(2s^2)(2p^6)(3s^2)(3p^6)(4s^2)
The electron "shell" that loses the electrons is the ...
Solution identifies what each element is and explains the element's electron configuration and the likely charge(s) when that element forms an ion.