Final answer:
A molecule with two lone pairs and four bonding regions around a central atom has an octahedral electron-pair geometry, but the molecular structure is square planar to minimize repulsions. Lone pairs occupy more space and significantly affect molecular shape.
Step-by-step explanation:
When dealing with molecules and their shapes, the VSEPR (Valence Shell Electron Pair Repulsion) theory comes into play. According to the question, a molecule with an octahedral electron-pair geometry and two lone pairs results in a square planar molecular structure. This structure arranges the six regions of electron density (four atoms and two lone pairs) around a central atom in an optimal manner to minimize lone pair-lone pair repulsions, as per the octahedral arrangement.
Therefore, although the central atom initially is surrounded by an octahedral arrangement of electron pairs, the presence of the two lone pairs on opposite sides of this octahedron (at 180° from each other) reduces the molecular geometry to square planar. This is due to the fact that lone pairs require more space than bonding pairs, and their positioning is crucial in determining the final shape of the molecule.