Explains the shape of `I_(3)^(-)` ion.

Explanation

The outer shell electronic configuration (in the ground state) of the central 1 atom is `5s^(2)5p_(x)^(2)5p_(y)^(2)5p_(z)^(1)5d^(0)`. It undergoes `sp^(3)d`-hybridisation. Out of the five `sp^(3)d` hybrid orbital, one is half-filled, one is empty and the remaining three are fully-filled. the half-filled orbital forms covalent bond with the iodine atomm. the vacant orbital accepts an electron pair for the `I^(-)` ion to form a coordinate bond. the remaining three fully-filled orbitals occupy equatorial positions. thus, the geometry of three lone pairs and two bond pairs is trigonal bipyramidal and the shape of the `I_(3)^(-)` ion is linear as shown in the figure.