Which of the following has highest first ionization potential among Ne, Mg, Cl and Na

Chlorine (Cl)

Explanation:

Because the shielding effect (by the inner electrons) remains the same but the nuclear charge is increasing (due to the increasing number of protons)

So Chlorine has the highest number of protons ... so its outter electrons tend to expierence the most nuclear attraction hence making it more harder to remove the first electron