Answer. 4s
Ca = Calcium Atomic number is 20, that means it has 20 proton and 20 electron.
1s2,2s2,2p6,3s2,3p6,and 4s2, total of 20 electrons, therefore Highest occupied energy level of Ca is 4s
Carbon's highest energy level is the second, more particularly the 2p orbital.
2p
5s
90
2s2
Alkali metals
Helium has the highest ionization energy.
Sr has two electrons in the highest occupied energy level
There are two electrons.
The valence electron shell of noble gases is full.
5s
The 3rd energy level is the highest occupied energy level for chlorine with seven electrons.
90
Beryllium will have the highest. Down a group ionization energy decreases.
Alkali metals
2
1s
2s2
Helium has the highest ionization energy.