Which of the following tetrahalides does not exist?

Group-14 elements can form halides of formula ${\mathrm{MX}}_2$ and ${\mathrm{MX}}_4$ (where $\mathrm{X} = \mathrm{F}, \mathrm{Cl}, \mathrm{Br}, \mathrm{I}$). Except carbon, all other members react directly with halogen under suitable condition to make halides. Most of the ${\mathrm{MX}}_4$ are covalent in nature. The central metal atom in these halides undergoes ${\mathrm{sp}}^3$ hybridisation and the molecule is tetrahedral in shape.  ${\mathrm{PbI}}_4$ does not exist because $\mathrm{Pb}—\mathrm{I}$ bond initially formed during the reaction does not release enough energy to unpair $6{\mathrm{s}}^2$ electrons and excite one of them to higher orbital to have four unpaired electrons around lead atom.