Concept: VSEPR theory is used to predict the geometry of molecules based on the repulsion between electron pairs around the central atom. For molecules with 5 electron domains (5 bond pairs and 0 lone pairs), the electron geometry and molecular geometry are both trigonal bipyramidal.

Why (D) is correct:

PCl₅ has a central phosphorus atom bonded to five chlorine atoms. According to VSEPR theory, the phosphorus atom has five bond pairs and no lone pairs. This arrangement leads to a trigonal bipyramidal geometry to minimize electron-pair repulsion. In a trigonal bipyramidal geometry, there are two types of bonds: axial and equatorial. The three equatorial bonds lie in a plane, making angles of 120° with each other, while the two axial bonds are perpendicular to this plane.

Option Analysis:

• A) The geometry of PCl₅ is square pyramidal. This is incorrect. Square pyramidal geometry occurs when there are 5 bond pairs and 1 lone pair (e.g., BrF₅), or 4 bond pairs and 1 lone pair (e.g., SF₄). PCl₅ has 5 bond pairs and 0 lone pairs.
• B) Axial bonds are shorter than equatorial bonds. This is incorrect. In trigonal bipyramidal geometry, the axial bonds experience more repulsion from the three equatorial bond pairs than the equatorial bonds experience from the two axial bond pairs. To minimize this repulsion, the axial bonds are slightly longer and weaker than the equatorial bonds.
• C) PCl₅ has non-zero net dipole moment. This is incorrect. PCl₅ has a symmetrical trigonal bipyramidal geometry. The bond dipoles cancel each other out due to this symmetry, resulting in a net dipole moment of zero, making the molecule nonpolar.
• D) The geometry of PCl₅ is trigonal bipyramidal. This is correct, as explained above.

Correct Answer: (D)