Give the formula and describe the structure of a noble gas species which is isostructural with :
`(i) ICI_(4)^(-) (ii) Ibr_(2)^(-) (iii) BrO_(3)^(-)`

Explanation

(i) Structure of `ICI_(4)^(-)`. The central I atom has in all 8 electrons (7 valence electrons `+1` due to negative charge). Out of these, it shares 4 electrons with four atoms of Cl and the remaining four electrons constitute two lone pairs. In all, there are six pairs. The structure of the ion must be octahedral or distorted square planar in order to minimise the forces of repulsion among the two electrons pairs. `ICl_(4)^(-) " has" (7+4xx7+1)=36` valence electrons and it iso-electronic and iso-structural with `XeF_(4) (8+4xx7)` which has also 36 valence electrons.
(ii) Structure of `IBr_(2)^(-)`. In `IBr_(2)^(-)` ion, the central I atom has 8 valence electrons `(7+1)`. Out of these, it shares 2 electrons with two atoms of Br and the remaining 6 electrons constitute three lone pairs. In all, there are five pairs. The structure of the ion must be trigonal bipyramidal or linear in order to minimise the force of repulsion among the three lone electrons pairs. `IBr_(2)^(-)` has `(7+2xx7+1)=22` valence electrons and is isoelectronic as well as iso-structural with noble gas species `XeF_(2)` which has also `22(8+2xx7)` electrons.
(iii) Structure of `BrO_(3)^(-)` ion. In `BrO_(3)^(-)` ion, the central Br atom has 8 valence electrons `(7+1)`. Out of these, it shares 4 with two atoms of O forming Br=O bonds. Out of the remaining four electrons, 2 are donated to the third O atom and account for its negative charge. The remaining 2 eletrons constitute one lone pair. In order to minimise the force of repulsion, the structure of `BrO_(3)^(-)` ion must be pyramidal . `BrO_(3)^(-)` ion has `(7+3xx6+1)=26` valence electrons and is isoelectronic as well as iso-structural with noble gas species `XeO_(3)` which has also `26 (8+3xx6)` electrons.