Final answer:
The electron pair geometry (EPG) and the molecular structure (MS) are determined by the regions of electron density and lone pairs: Trigonal bipyramidal EPG forms a T-shaped MS, octahedral EPG forms a square planar MS, tetrahedral EPG forms a trigonal pyramidal MS, and linear EPG results in a linear MS.
Step-by-step explanation:
The electron pair geometry and molecular structure of ions can be predicted based on the number of regions of electron density around the central atom and the number of lone pairs affecting the molecule's shape. In trigonal bipyramidal electron-pair geometry, if there are two lone pairs, the molecular structure is T-shaped.
For octahedral electron-pair geometry with two lone pairs, the molecule adopts a square planar structure. A tetrahedral electron-pair geometry with one lone pair will have a trigonal pyramidal molecular structure, and a molecule with linear electron-pair geometry will also have a linear molecular structure.