A solution of (–$$l$$) – chloro –1 – phenylethane in toluene racemises slowly in the presence of a small amount of SbCl₅, due to the formation of :

In which of the following pairs of molecules/ions, both the species are not likely to exist?

Stability of the species Li₂, $$Li_2^−$$ and $$Li_2^+$$ increases in the order of:

Which one of the following molecules is expected to exhibit diamagnetic behaviour?