The ionization or ionization energy is the process wherein the energy necessary to remove an electron from the neutral atom. When located in the periodic table, it increases across the row and decreases going down. The ionization energy is greatest for the noble gases. For example, the ionization energy for fluorine is 1681.6 kJ/mol. It means that it takes 1681.6 kJ/mol of fluorine to completely remove an electron or ionize it. The answer is d. losing or gaining electrons.