Chapter 7 - Atomic Structure and Periodicity - Exercises - Page 346: 108

a. $Rb < Na < Be$ b. $Sr < Se < Ne$ c. $Fe < P < O$

a. The first ionization energy generally decreases with a higher principal quantum number and less number of valence electrons. Therefore, the order is $Rb < Na < Be$. b. The first ionization energy generally decreases with a higher principal quantum number and less number of valence electrons. Therefore, the order is $Sr < Se < Ne$. c. The first ionization energy generally decreases with a higher principal quantum number and less number of valence electrons. Therefore, the order is $Fe < P < O$.