Electronic Configuration
From Nitrogen (N) to Magnesium (Mg)
Electronic configuration of Nitrogen
Atomic number of nitrogen = 7.
Therefore number of electrons = 7
Thus, electronic configuration of nitrogen is 
Number of orbit in nitrogen = 2
Electronic configuration of Oxygen
Atomic number of oxygen = 8.
Therefore number of electrons = 8.
Thus, electronic configuration of oxygen is 
Number of orbit in oxgyen = 2
Electronic configuration of Fluorine
Atomic number of fluorine = 9
Therefore number of electrons = 9
Thus, electronic configuration of fluorine is 
Number of orbit in fluorine = 2
Electronic configuration of Neon
Atomic number of neon = 10
Therefore number of electrons = 10
Thus, electronic configuration of neon is 
Number of orbit in Neon = 2
Electronic configuration of Sodium
Atomic number of sodium = 11
Therefore number of electrons = 11
Since, in 2nd orbit the maximum number of electrons is equal to 8 and there are 11 electrons in sodium atom, thus the eleventh electron will go in third orbit.
Thus, electronic configuration of sodium is 
Number of orbit in sodium = 3
Electronic configuration of Magnesium
Atomic number of magnesium = 12
Therefore number of electrons = 12
Thus, electronic configuration of magnesium is 
Number of orbit in magnesium = 3.