Question

from which atom is it hardest to remove an electron? (highest ionization energy)
o s
o al
o mg
o f

Explanation:

Step1: Recall ionization energy trend

Ionization energy increases across a period and decreases down a group in the periodic table.

Step2: Locate elements in periodic table

S (sulfur) is in group 16, period 3; Al (aluminum) is in group 13, period 3; Mg (magnesium) is in group 2, period 3; F (fluorine) is in group 17, period 2.

Step3: Compare ionization energies

Fluorine is the most electronegative element and has a high effective nuclear charge. It is in the upper - right of the periodic table among these elements, so it has the highest ionization energy.

Answer:

F