Final answer:
PI3 has a tetrahedral electron-group geometry due to four electron groups around the phosphorus atom. However, the molecular shape is trigonal pyramidal because one of these groups is a lone pair.
Step-by-step explanation:
The molecule PI3 is phosphorus triiodide, and its molecular geometry can be understood by considering the number of valence electrons and the electron group geometry around the phosphorus atom.
Phosphorus has one lone pair and is bonded to three iodine atoms, which means it has four electron groups.
This corresponds to a tetrahedral electron-group geometry.
However, because of the lone pair, the actual shape of the molecule is trigonal pyramidal, similar to ammonia (NH3). So, the correct answer is B. trigonal pyramidal.