A student was using the periodic table to organize elements based on their ionization energy from lowest to highest. At the end of the class period, the student left one of the 4 spaces blank. It looked like this: Barium (Ba), Cobalt (Co), , Helium (He)

There are 4 options to fill in the blank: Antimony (Sb), Krypton (Kr), Selenium (Se), or Nitrogen (N). Which element is the correct one to fill in the blank? Explain why using the following words: ionization energy, attractive force, energy levels, distance, and protons.