\(\eqalign{ & Z = 20:\,\,1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2} \cr & Z = 21:\,\,1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^1}4{s^2} \cr & Z = 22:\,\,1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^2}4{s^2} \cr & Z = 24:\,\,1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^1} \cr & Z = 29:\,\,1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^1}. \cr}\)