All the five bonds in `PCl_5` are not equivalent justify.

Explanation

Ground state electronic configuration of phosphorus (Z - 15) is as follows:
`P(Z=15) : 1s^2 2s^1 2p^6 3s^2 3p_x^1 3p_y^1 p_z^1`
To form five bonds in `PCl_5`, the pair of electrons in 3s-orbital unpair with the promotion of one electron to empty 3d-orbital. This is followed by `sp^3 d` hybridisation which gives five half filled equivalent orbitals for the formation of five sigma bonds with five chlorine atoms. Thus `PCl_5` has trigonal bipyramidal geometry. In `PCl_5` the three equatorial P-Cl bonds are equivalent while the two .axial. bonds are different. The two axial P-Cl bonds are longer than three equatorial P-Cl bonds, due to repulsion caused by equitorial bonded pairs of electron.