Final answer:
The number of 90° interactions at an axial site depends on the placement of electron pairs. No 90° interactions occur with only axial lone pairs, while one axial and one equatorial lone pair yield one LP-LP and three LP-BP repulsions at 90°. The scenario in the question likely describes this latter arrangement.
Step-by-step explanation:
The axial sites in molecular geometry refer to the positions in a molecule that are aligned with the central atom's axis. In the context of VSEPR theory, or Valence Shell Electron Pair Repulsion theory, the axial site's interactions with lone pairs (LP) and bonding pairs (BP) are considered when predicting molecular shapes. The number of 90° interactions at an axial site depends on the arrangement of electron pairs around the central atom.
If the lone pairs are placed at the axial positions (axiam), there are no LP-LP interactions at 90°, and similarly, no 90° LP-BP interactions occur. When lone pairs are positioned equatorially, there are zero 90° LP-LP interactions, but there are four 90° LP-BP interactions. If the lone pairs are distributed such that one is in an axial position and the other is equatorial, there is one 90° LP-LP interaction and three 90° LP-BP interactions.
For molecules with different electron pair arrangements, like AX3E2, which has three bonding pairs and two lone pairs, the repulsions and interactions at axial sites can differ. Placing both lone pairs axially results in six LP-BP repulsions at 90°, whereas one axial lone pair and one equatorial lone pair yields one 90° LP-LP repulsion and three LP-BP repulsions at 90°. In conclusion, the axial site has potentially different numbers of 90° interactions depending on the specific arrangement of electron pairs.