$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^5$  is the electronic configuration of

The given electronic configuration indicates that there is total 17 electrons are  present in it. The neutral atom of an element with 17 electrons is chlorine (Cl) . Since its atomic number (Z) is 17.