Find number of ions which does not have (18 + 2) electronic configuration :

${\mathrm{Zn}}^{2+},{\mathrm{Cu}}^{2+},{\mathrm{Fe}}^{2+},{\mathrm{Sn}}^{2+},{\mathrm{Sn}}^{4+},{\mathrm{Tl}}^{+},{\mathrm{T}}^{3+}$

 ${\mathrm{T}}^{3+}$ and ${\mathrm{Sn}}^{2+}$ are the ions which has (18 + 2) electronic configuration. The ions which do not have such configuration are,

${\mathrm{Zn}}^{2+},{\mathrm{Cu}}^{2+},{\mathrm{Fe}}^{2+},{\mathrm{Sn}}^{4+},{\mathrm{Tl}}^{3+}$

Thus, correct answer is 5.