Question

what has the greatest ionization energy?
mg
ca
na
k

Explanation:

Ionization energy generally increases across a period and decreases down a group in the periodic table. Mg is in Group 2 and Period 3, Ca is in Group 2 and Period 4, Na is in Group 1 and Period 3, and K is in Group 1 and Period 4. Mg has a higher ionization energy than Na as it is in Group 2 with a smaller atomic radius and more protons attracting the outer - shell electrons. Mg also has a higher ionization energy than Ca and K because they are in a lower period with electrons further from the nucleus and thus easier to remove.

Answer:

Mg