The hybridization of $I$  in ${\mathrm{ICl}}_2^{-}$ is

3. There are 3 x 7 + 1 = 22 valence electrons in ${\mathrm{ICl}}_2^{-}$. These are distributed as

Due to five pairs of electrons around I, the hybridization of l will be  $s{p}^{3}d$.