D. Potassium has a lower ionization energy than sodium
Ionization energy = amount of energy it takes for an atom to LOSE an electron (so A is proven wrong already)
Why B and C are wrong: Ionization energy increases the closer the electrons are to the nucleus, so ionization energy increases as you go up and to the right on your periodic table. I remember that Fluorine (top right element on periodic table that is not a noble gas, those guys are weird) has the highest ionization energy.