The number of s-electrons present in an ion with 55 protons in its...

The atom with 55 protons is caesium(Cs). The electronic configuration of Cs is $1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}4{s}^{2}3{d}^{10}4{p}^{6}5{s}^{2}4{d}^{10}5{p}^{6}6{s}^{1}$.

The mono positive ion means one electron is removed from outermost orbital. Hence, the sum of electrons in $1s, 2s, 3s, 4s, 5s$ orbitals are$10$.