Explanation

(b)
The atomic number of cesium is 55. The electronic configuration of cesium atom is
$\ _{55}Cs = 1s^{2},2s^{2}2p^{6},3s^{2}3p^{6},4s^{2},{3d}^{10}4p^{6},5s^{2},4d^{10},5p^{6},6s^{1}$
The electronic configuration of cesium atom is
$Cs^{+} = 1s^{2},2s^{2}2p^{6},3s^{2}3p^{6}3d^{10},4s^{2}4p^{6}4d^{10},5s^{2}5p^{6},6s^{0}$
So, the total number of $s$-electrons =10,
The total number of $p$-electrons=24,
The total number of $d$-electrons=20