Which of the following two species in the pair are isostructural : -

$XeF_2$: Xe has 2 bond pairs and 3 lone pairs ($sp^3d$), so it is linear. $IF_2^-$: I has 2 bond pairs and 3 lone pairs, also linear. They are isostructural.
$NH_3$ is pyramidal (3 bp + 1 lp), while $BF_3$ is trigonal planar (3 bp, no lp).
$CO_3^{2-}$ is trigonal planar, while $SO_3^{2-}$ is pyramidal (S has a lone pair).
$PCl_5$ is trigonal bipyramidal, while $ICl_5$ is square pyramidal (5 bp + 1 lp).
So $XeF_2$ and $IF_2^-$ are isostructural.