The hybridisation scheme for the central atom includes a d -orbital...

$\mathrm{I}_3^{-}$ is linear with central iodine atom undergoing $s p^3 d$-hybridisation and three lone pairs occupying equatorial position. Thus, this structure include $d$-orbital contribution to the hybridisation scheme. The structure is, $\mathrm{PCl}_3$ structure is $s p^3$-hybridised with one lone pair. $\mathrm{NO}_3^{-}$ is $s p^2$-hybridised and $\mathrm{H}_2 \mathrm{Se}$ is $s p^3$ - hybridised with two lone pairs of Se atom.