Gaseous PCl5 contains two distinct P–Cl bond lengths. Which statement best accounts for the difference?
a) Axial P–Cl bonds are shorter because atoms in a straight line allow maximal orbital overlap.
b) Equatorial P–Cl bonds are shorter because d–pπ-backbonding strengthens the equatorial bonds.
c) Axial P–Cl bonds are longer because each experiences three 90∘ interactions with equatorial bonds, increasing repulsion and weakening the bond.
d) All P–Cl bonds are the same length; any apparent difference is due to experimental error.