Hybridisation is defined as the phenomenon of mixing of orbitals of nearly the same energy so as to redistribute their energies and to give rise to new orbitals of equivalent energy. It is the valence shell atomic which get hybridised one of the electrons from an orbital in the ground state electronic configuration of the atom gets promoted to the next available orbital of higher energy resulting in an excited state electronic configuration with the appropriate number of half filled orbitals. The orbitale in the excited state undergo hybridisation giving hybrid orbilats of equivalent energy. Hybrid orbitals generally from either bonds or contain lone pair of electrons, they do not form $\pi$ bonds. Depending on the type of orbitals used the hybridisation may be categorized as $SP$(linear), $SP^2$ (trigonal planar ), $SP^3$(tetrahedral), $SP^3d$(trigonal bipyramidal), $SP^3d^2$(Octahedral), $SP^3d^3$ (Pentagonal bipyramid ). Which one of the following species is diamagnetic ?