Which of the following statements about ionization energy is true?
a. in a period, elements farther to the right generally have lower ionization energies than elements on the left.
b. elements toward the bottom of a group periodic table generally have higher ionization energies than elements at the top of the group.
c. ionization energy is the amount of energy used to add an electron to an atom.
d. potassium has a lower ionization energy than sodium.