Explanation:
Ionization energy is defined as the energy required to remove the most loosely bound electron from a neutral gaseous atom.
With increase in atomic size of the atom, there will be less force of attraction between the nucleus and the valence electrons of the atom. Hence, with lesser amount of energy the valence electrons can be removed.
Na, Mg, Al, Si, and P are all period 3 elements. Hence, there will be decrease in size from sodium to phosphorous. So, the amount of enenrgy required to remove an electron from phosphorous atom will be high as it is smaller is size.
And, when one electron is removed from it then it further decreases in size. So, when second electron is removed then we need to provide much more heat energy to overcome the strong force of attraction between the nucleus and valence electrons.
Thus, we can conclude that out of the given options P element has the highest second ionization energy.
