Question

In which of the following molecules, all bond lengths are not equal?

• A. SF$_6$
• B. PCl$_5$
• C. BCl$_3$
• D. CCl$_4$

Hint:

In molecules with different bond positions (like trigonal bipyramidal), axial bonds are usually longer than equatorial bonds.

Answer 1

The Correct Option is B

Step 1: Molecular Geometry Analysis
PCl$_5$ exhibits a trigonal bipyramidal geometry, characterized by two distinct bond positions: axial and equatorial.
Chlorine atoms in the equatorial plane form bonds at \( 120^\circ \), while axial chlorine atoms are positioned at \( 90^\circ \) relative to the equatorial bonds.
Step 2: Bond Length Discrepancy
Repulsive forces result in longer axial bonds compared to equatorial bonds.
The increased repulsion experienced by axial bonds from equatorial bonds leads to their elongation.
Conclusion: The trigonal bipyramidal structure of PCl$_5$ results in inequal bond lengths.