Effective nuclear charge Z* increases very slowly down a group for the “valence” i.e. outermost orbital but increases rapidly along a period For 1st part, Answer b part Li, Be, B, C So for 2nd ->a part answer is Na,K,Rb,Cs Solution Effective nuclear charge Z* increases very slowly down a group for the “valence” i.e. outermost orbital but increases rapidly along a period For 1st part, Answer b part Li, Be, B, C So for 2nd ->a part answer is Na,K,Rb,Cs.