Answer:
Na < Al < Mg < S < Cl
Step-by-step explanation:
Sodium has the smallest ionization energy because it wants to lose an electron as an alkali metal.
Aluminum has the second smallest because losing an electron would leave it with just a full s orbital.
Magnesium has the third smallest because although it's removing an electron from a full s orbital, it has less protons than sulfur and chlorine to keep the electron in the shell.
Sulfur has the second largest because it has more protons to pull at the electrons.
Chlorine has the largest ionization energy because it really wants an electron to fill the p orbital. Due to its number of protons, the element is also very small and it will be difficult to remove an electron.