The more reactivity of Phosphorouspentachloride $(PCl_5)$ is due to

Question

$\begin{array}{1 1}(a)\;\text{ equatorial bonds are slightly longer than the axial bonds}\\(b)\;\text{axial bonds are stronger than the equatorial bonds}\\(c)\;\text{ axial bonds are slightly longer than the equatorial bonds}\\(d)\;\text{ axial bonds are slightly stronger and slightly shorter than the equatorial bonds}\end{array}$