Which of the following statements best explains the differences in first ionization energies between krypton and rubidium?
A.
Rubidium's nuclear charge is greater than krypton's.
B.
The distance from the nucleus to the outermost electron is greater in krypton than it is in rubidium.
C.
The distance from the nucleus to the outermost electron is smaller in krypton than it is in rubidium.
D.
Rubidium's nuclear charge is smaller than krypton's.